Multiple imputation strategies for missing event times in a multi-state model analysis

In clinical studies, multi-state model (MSM) analysis is often used to describe the sequence of events that patients experience, enabling better understanding of disease progression. A complicating factor in many MSM studies is that the exact event times may not be known. Motivated by a real dataset of patients who received stem cell transplants, we considered the setting in which some event times were exactly observed and some were missing. In our setting, there was little information about the time intervals in which the missing event times occurred and missingness depended on the event type, given the analysis model covariates. These additional challenges limited the usefulness of some missing data methods (maximum likelihood, complete case analysis, and inverse probability weighting). We show that multiple imputation (MI) of event times can perform well in this setting. MI is a flexible method that can be used with any complete data analysis model. Through an extensive simulation study, we show that MI by predictive mean matching (PMM), in which sampling is from a set of observed times without reliance on a specific parametric distribution, has little bias when event times are missing at random, conditional on the observed data. Applying PMM separately for each sub-group of patients with a different pathway through the MSM tends to further reduce bias and improve precision. We recommend MI using PMM methods when performing MSM analysis with Markov models and partially observed event times.

Time-sensitive testing pressures and COVID-19 outcomes: are socioeconomic inequalities over the first year of the pandemic explained by selection bias?

BACKGROUND

There are many ways in which selection bias might impact COVID-19 research. Here we focus on selection for receiving a polymerase-chain-reaction (PCR) SARS-CoV-2 test and how known changes to selection pressures over time may bias research into COVID-19 infection.

METHODS

Using UK Biobank (N = 420,231; 55% female; mean age = 66.8 [SD = 8·11]) we estimate the association between socio-economic position (SEP) and (i) being tested for SARS-CoV-2 infection versus not being tested (ii) testing positive for SARS-CoV-2 infection versus testing negative and (iii) testing negative for SARS-CoV-2 infection versus not being tested. We construct four distinct time-periods between March 2020 and March 2021, representing distinct periods of testing pressures and lockdown restrictions and specify both time-stratified and combined models for each outcome. We explore potential selection bias by examining associations with positive and negative control exposures.

RESULTS

The association between more disadvantaged SEP and receiving a SARS-CoV-2 test attenuated over time. Compared to individuals with a degree, individuals whose highest educational qualification was a GCSE or equivalent had an OR of 1·27 (95% CI: 1·18 to 1·37) in March-May 2020 and 1·13 (95% CI: 1.·10 to 1·16) in January-March 2021. The magnitude of the association between educational attainment and testing positive for SARS-CoV-2 infection increased over the same period. For the equivalent comparison, the OR for testing positive increased from 1·25 (95% CI: 1·04 to 1·47), to 1·69 (95% CI: 1·55 to 1·83). We found little evidence of an association between control exposures, and any considered outcome.

CONCLUSIONS

The association between SEP and SARS-CoV-2 testing changed over time, highlighting the potential of time-specific selection pressures to bias analyses of COVID-19. Positive and negative control analyses suggest that changes in the association between SEP and SARS-CoV-2 infection over time likely reflect true increases in socioeconomic inequalities.

Quantitative bias analysis in practice: review of software for regression with unmeasured confounding

BACKGROUND

Failure to appropriately account for unmeasured confounding may lead to erroneous conclusions. Quantitative bias analysis (QBA) can be used to quantify the potential impact of unmeasured confounding or how much unmeasured confounding would be needed to change a study's conclusions. Currently, QBA methods are not routinely implemented, partly due to a lack of knowledge about accessible software. Also, comparisons of QBA methods have focused on analyses with a binary outcome.

METHODS

We conducted a systematic review of the latest developments in QBA software published between 2011 and 2021. Our inclusion criteria were software that did not require adaption (i.e., code changes) before application, was still available in 2022, and accompanied by documentation. Key properties of each software tool were identified. We provide a detailed description of programs applicable for a linear regression analysis, illustrate their application using two data examples and provide code to assist researchers in future use of these programs.

RESULTS

Our review identified 21 programs with [Formula: see text] created post 2016. All are implementations of a deterministic QBA with [Formula: see text] available in the free software R. There are programs applicable when the analysis of interest is a regression of binary, continuous or survival outcomes, and for matched and mediation analyses. We identified five programs implementing differing QBAs for a continuous outcome: treatSens, causalsens, sensemakr, EValue, and konfound. When applied to one of our illustrative examples, causalsens incorrectly indicated sensitivity to unmeasured confounding whereas the other four programs indicated robustness. sensemakr performs the most detailed QBA and includes a benchmarking feature for multiple unmeasured confounders.

CONCLUSIONS

Software is now available to implement a QBA for a range of different analyses. However, the diversity of methods, even for the same analysis of interest, presents challenges to their widespread uptake. Provision of detailed QBA guidelines would be highly beneficial.

Exploring the impact of selection bias in observational studies of COVID-19: a simulation study

BACKGROUND

Non-random selection of analytic subsamples could introduce selection bias in observational studies. We explored the potential presence and impact of selection in studies of SARS-CoV-2 infection and COVID-19 prognosis.

METHODS

We tested the association of a broad range of characteristics with selection into COVID-19 analytic subsamples in the Avon Longitudinal Study of Parents and Children (ALSPAC) and UK Biobank (UKB). We then conducted empirical analyses and simulations to explore the potential presence, direction and magnitude of bias due to this selection (relative to our defined UK-based adult target populations) when estimating the association of body mass index (BMI) with SARS-CoV-2 infection and death-with-COVID-19.

RESULTS

In both cohorts, a broad range of characteristics was related to selection, sometimes in opposite directions (e.g. more-educated people were more likely to have data on SARS-CoV-2 infection in ALSPAC, but less likely in UKB). Higher BMI was associated with higher odds of SARS-CoV-2 infection and death-with-COVID-19. We found non-negligible bias in many simulated scenarios.

CONCLUSIONS

Analyses using COVID-19 self-reported or national registry data may be biased due to selection. The magnitude and direction of this bias depend on the outcome definition, the true effect of the risk factor and the assumed selection mechanism; these are likely to differ between studies with different target populations. Bias due to sample selection is a key concern in COVID-19 research based on national registry data, especially as countries end free mass testing. The framework we have used can be applied by other researchers assessing the extent to which their results may be biased for their research question of interest.

Sample-constrained partial identification with application to selection bias

Many partial identification problems can be characterized by the optimal value of a function over a set where both the function and set need to be estimated by empirical data. Despite some progress for convex problems, statistical inference in this general setting remains to be developed. To address this, we derive an asymptotically valid confidence interval for the optimal value through an appropriate relaxation of the estimated set. We then apply this general result to the problem of selection bias in population-based cohort studies. We show that existing sensitivity analyses, which are often conservative and difficult to implement, can be formulated in our framework and made significantly more informative via auxiliary information on the population. We conduct a simulation study to evaluate the finite sample performance of our inference procedure and conclude with a substantive motivating example on the causal effect of education on income in the highly-selected UK Biobank cohort. We demonstrate that our method can produce informative bounds using plausible population-level auxiliary constraints. We implement this method in the R package selectioninterval.

Using linear and natural cubic splines, SITAR, and latent trajectory models to characterise nonlinear longitudinal growth trajectories in cohort studies

BACKGROUND

Longitudinal data analysis can improve our understanding of the influences on health trajectories across the life-course. There are a variety of statistical models which can be used, and their fitting and interpretation can be complex, particularly where there is a nonlinear trajectory. Our aim was to provide an accessible guide along with applied examples to using four sophisticated modelling procedures for describing nonlinear growth trajectories.

METHODS

This expository paper provides an illustrative guide to summarising nonlinear growth trajectories for repeatedly measured continuous outcomes using (i) linear spline and (ii) natural cubic spline linear mixed-effects (LME) models, (iii) Super Imposition by Translation and Rotation (SITAR) nonlinear mixed effects models, and (iv) latent trajectory models. The underlying model for each approach, their similarities and differences, and their advantages and disadvantages are described. Their application and correct interpretation of their results is illustrated by analysing repeated bone mass measures to characterise bone growth patterns and their sex differences in three cohort studies from the UK, USA, and Canada comprising 8500 individuals and 37,000 measurements from ages 5-40 years. Recommendations for choosing a modelling approach are provided along with a discussion and signposting on further modelling extensions for analysing trajectory exposures and outcomes, and multiple cohorts.

RESULTS

Linear and natural cubic spline LME models and SITAR provided similar summary of the mean bone growth trajectory and growth velocity, and the sex differences in growth patterns. Growth velocity (in grams/year) peaked during adolescence, and peaked earlier in females than males e.g., mean age at peak bone mineral content accrual from multicohort SITAR models was 12.2 years in females and 13.9 years in males. Latent trajectory models (with trajectory shapes estimated using a natural cubic spline) identified up to four subgroups of individuals with distinct trajectories throughout adolescence.

CONCLUSIONS

LME models with linear and natural cubic splines, SITAR, and latent trajectory models are useful for describing nonlinear growth trajectories, and these methods can be adapted for other complex traits. Choice of method depends on the research aims, complexity of the trajectory, and available data. Scripts and synthetic datasets are provided for readers to replicate trajectory modelling and visualisation using the R statistical computing software.

Combining Longitudinal Data From Different Cohorts to Examine the Life-Course Trajectory

Longitudinal data are necessary to reveal changes within an individual as he or she ages. However, rarely will a single cohort study capture data throughout a person's entire life span. Here we describe in detail the steps needed to develop life-course trajectories from cohort studies that cover different and overlapping periods of life. Such independent studies are probably from heterogenous populations, which raises several challenges, including: 1) data harmonization (deriving new harmonized variables from differently measured variables by identifying common elements across all studies); 2) systematically missing data (variables not measured are missing for all participants in a cohort); and 3) model selection with differing age ranges and measurement schedules. We illustrate how to overcome these challenges using an example which examines the associations of parental education, sex, and race/ethnicity with children's weight trajectories. Data were obtained from 5 prospective cohort studies (carried out in Belarus and 4 regions of the United Kingdom) spanning data collected from birth to early adulthood during differing calendar periods (1936-1964, 1972-1979, 1990-2012, 1996-2016, and 2007-2015). Key strengths of our approach include modeling of trajectories over wide age ranges, sharing of information across studies, and direct comparison of the same parts of the life course in different geographical regions and time periods. We also introduce a novel approach of imputing individual-level covariates of a multilevel model with a nonlinear growth trajectory and interactions.

Multiple imputation strategies for a bounded outcome variable in a competing risks analysis

In patient follow-up studies, events of interest may take place between periodic clinical assessments and so the exact time of onset is not observed. Such events are known as "bounded" or "interval-censored." Methods for handling such events can be categorized as either (i) applying multiple imputation (MI) strategies or (ii) taking a full likelihood-based (LB) approach. We focused on MI strategies, rather than LB methods, because of their flexibility. We evaluated MI strategies for bounded event times in a competing risks analysis, examining the extent to which interval boundaries, features of the data distribution and substantive analysis model are accounted for in the imputation model. Candidate imputation models were predictive mean matching (PMM); log-normal regression with postimputation back-transformation; normal regression with and without restrictions on the imputed values and Delord and Genin's method based on sampling from the cumulative incidence function. We used a simulation study to compare MI methods and one LB method when data were missing at random and missing not at random, also varying the proportion of missing data, and then applied the methods to a hematopoietic stem cell transplantation dataset. We found that cumulative incidence and median event time estimation were sensitive to model misspecification. In a competing risks analysis, we found that it is more important to account for features of the data distribution than to restrict imputed values based on interval boundaries or to ensure compatibility with the substantive analysis by sampling from the cumulative incidence function. We recommend MI by type 1 PMM.

Mendelian randomisation with coarsened exposures

A key assumption in Mendelian randomisation is that the relationship between the genetic instruments and the outcome is fully mediated by the exposure, known as the exclusion restriction assumption. However, in epidemiological studies, the exposure is often a coarsened approximation to some latent continuous trait. For example, latent liability to schizophrenia can be thought of as underlying the binary diagnosis measure. Genetically driven variation in the outcome can exist within categories of the exposure measurement, thus violating this assumption. We propose a framework to clarify this violation, deriving a simple expression for the resulting bias and showing that it may inflate or deflate effect estimates but will not reverse their sign. We then characterise a set of assumptions and a straight‐forward method for estimating the effect of SD increases in the latent exposure. Our method relies on a sensitivity parameter which can be interpreted as the genetic variance of the latent exposure. We show that this method can be applied in both the one‐sample and two‐sample settings. We conclude by demonstrating our method in an applied example and reanalysing two papers which are likely to suffer from this type of bias, allowing meaningful interpretation of their effect sizes.

Bootstrap inference for multiple imputation under uncongeniality and misspecification

Multiple imputation has become one of the most popular approaches for handling missing data in statistical analyses. Part of this success is due to Rubin’s simple combination rules. These give frequentist valid inferences when the imputation and analysis procedures are so-called congenial and the embedding model is correctly specified, but otherwise may not. Roughly speaking, congeniality corresponds to whether the imputation and analysis models make different assumptions about the data. In practice, imputation models and analysis procedures are often not congenial, such that tests may not have the correct size, and confidence interval coverage deviates from the advertised level. We examine a number of recent proposals which combine bootstrapping with multiple imputation and determine which are valid under uncongeniality and model misspecification. Imputation followed by bootstrapping generally does not result in valid variance estimates under uncongeniality or misspecification, whereas certain bootstrap followed by imputation methods do. We recommend a particular computationally efficient variant of bootstrapping followed by imputation.

Accounting for missing data in statistical analyses: multiple imputation is not always the answer

Background

Missing data are unavoidable in epidemiological research, potentially leading to bias and loss of precision. Multiple imputation (MI) is widely advocated as an improvement over complete case analysis (CCA). However, contrary to widespread belief, CCA is preferable to MI in some situations.

Methods

We provide guidance on choice of analysis when data are incomplete. Using causal diagrams to depict missingness mechanisms, we describe when CCA will not be biased by missing data and compare MI and CCA, with respect to bias and efficiency, in a range of missing data situations. We illustrate selection of an appropriate method in practice.

Results

For most regression models, CCA gives unbiased results when the chance of being a complete case does not depend on the outcome after taking the covariates into consideration, which includes situations where data are missing not at random. Consequently, there are situations in which CCA analyses are unbiased while MI analyses, assuming missing at random (MAR), are biased. By contrast MI, unlike CCA, is valid for all MAR situations and has the potential to use information contained in the incomplete cases and auxiliary variables to reduce bias and/or improve precision. For this reason, MI was preferred over CCA in our real data example.

Conclusions

Choice of method for dealing with missing data is crucial for validity of conclusions, and should be based on careful consideration of the reasons for the missing data, missing data patterns and the availability of auxiliary information.

Childhood neurodevelopmental difficulties and risk of adolescent depression: the role of irritability

BACKGROUND

Children with neurodevelopmental disorders are at increased risk of developing depression. Irritability predicts depression in the general population and is common in children with neurodevelopmental disorders. Thus, it is possible that irritability in children with neurodevelopmental disorders contributes to the link with later depression. This study aimed to (a) examine the association between childhood neurodevelopmental difficulties and adolescent depression and (b) test whether irritability explains this association.

METHODS

Children with any neurodevelopmental difficulty at the age of 7-9 (n = 1,697) and a selected, comparison group without any neurodevelopmental difficulty (n = 3,177) were identified from a prospective, UK population-based cohort, the Avon Longitudinal Study of Parents and Children. Neurodevelopmental difficulties were defined as a score in the bottom 5% of the sample on at least one measure of cognitive ability, communication, autism spectrum symptoms, attention-deficit/hyperactivity symptoms, reading or motor coordination. The Development and Well-Being Assessment measured parent-reported child irritability at the age of 7, parent-reported adolescent depression at the age of 10 and 13, and self-reported depression at the age of 15. Depression measures were combined, deriving an outcome of major depressive disorder (MDD) in adolescence. Logistic regression examined the association between childhood neurodevelopmental difficulties and adolescent MDD, controlling for gender. Path analysis estimated the proportion of this association explained by irritability. Analyses were repeated for individual neurodevelopmental problems.

RESULTS

Childhood neurodevelopmental difficulties were associated with adolescent MDD (OR = 2.11, 95% CI = 1.24, 3.60, p = .006). Childhood irritability statistically accounted for 42% of this association. On examining each neurodevelopmental difficulty separately, autistic, communication and ADHD problems were each associated with depression, with irritability explaining 29%-51% of these links.

CONCLUSIONS

Childhood irritability appears to be a key contributor to the link between childhood neurodevelopmental difficulties and adolescent MDD. High rates of irritability in children with autistic and ADHD difficulties may explain elevated rates of depression in the neurodevelopmental group.

Interventions to support shared decision making for hypertension: A systematic review of controlled studies

BACKGROUND

Hypertension (high blood pressure) is a common long-term health condition. Patient involvement in treating and monitoring hypertension is essential. Control of hypertension improves population cardiovascular outcomes. However, for an individual, potential benefits and harms of treatment are finely balanced. Shared decision making has the potential to align decisions with the preferences and values of patients.

OBJECTIVE

Determine the effectiveness of interventions to support shared decision making in hypertension.

SEARCH STRATEGY

Searches in MEDLINE, EMBASE, CINAHL, Web of Science and PsycINFO up to 30 September 2017.

ELIGIBILITY CRITERIA

Controlled studies evaluating the effects of shared decision-making interventions for adults with hypertension compared with any comparator in any setting and reporting any outcome measures.

RESULTS

Six studies (five randomized controlled trials) in European primary care were included. Main intervention components were as follows: training for health-care professionals, decision aids, patient coaching and a patient leaflet. Four studies, none at low risk of bias, reported a measure of shared decision making; the intervention increased shared decision making in one study. Four studies reported blood pressure between 6 months and 3 years after the intervention; there was no difference in blood pressure between intervention and control groups in any study. Lack of comparability between studies prevented meta-analysis.

CONCLUSIONS

Despite widespread calls for shared decision making to be embedded in health care, there is little evidence to inform shared decision making for hypertension, one of the most common conditions managed in primary care.

Plasma Exchange for Guillain-Barré Syndrome

The impact of plasma exchange (PE) on the treatment of severe Guillain-Barré syndrome (GBS) was studied by comparing all the 16 patients treated with PE in a London teaching hospital between January 1985 and August 1987, with 64 historical controls drawn from a series of patients observed during a prospective study in South East England in 1983 and 1984. There were no GBS-related deaths in the PE treated group but seven in the historical controls (2P = 0.39). The median duration of ventilation was only 20 days (range 7-64) in the PE group compared with 36 days (range 14-365) in the surviving patients in the control group (2P = 0.06, 95% confidence interval of difference in medians -36 to 0 days). The PE group walked earlier without aid (median 55.5 compared with 86 days, 2P = 0.04, 95% confidence interval of difference in medians -88 to -2 days). Three months after the onset of neuropathy all PE treated patients were able to walk with support or better, whereas 19 of the surviving historical controls were unable to walk even with support (2P = 0.009). The costs of PE were offset by savings in intensive care unit and hospital expenditure.

Socioeconomic differences in childhood BMI trajectories in Belarus

Objective

To examine associations of parental socioeconomic position with early-life offspring body mass index (BMI) trajectories in a middle-income country.

Subjects

Overall, 12,385 Belarusian children born 1996–97 and enrolled in a randomised breastfeeding promotion trial at birth, with 3–14 measurements of BMI from birth to 7 years.

Methods

Cohort analysis in which exposures were parental education (common secondary or less; advanced secondary or partial university; completed university) and occupation (manual; non-manual) at birth, and the outcome was BMI z-score trajectories estimated using multilevel linear spline models, controlling for trial arm, location, parental BMI, maternal smoking status and number of older siblings.

Results

Infants born to university-educated mothers were heavier at birth than those born to secondary school-educated mothers [by 0.13 BMI z-score units (95% confidence interval, CI: 0.07, 0.19) for girls and 0.11 (95% CI: 0.05, 0.17) for boys; equivalent for an infant of average birth length to 43 and 38 g, respectively]. Between the ages of 3–7 years children of the most educated mothers had larger BMI increases than children of the least educated mothers. At age 7 years, after controlling for trial arm and location,  children of university-educated mothers had higher BMIs than those born to secondary school-educated mothers by 0.11 z-score (95% CI: 0.03, 0.19) among girls and 0.18 (95% CI: 0.1, 0.27) among boys, equivalent to differences in BMI for a child of average height of 0.19 and 0.26 kg/m², respectively. After further controlling for parental BMI, these differences attenuated to 0.08 z-score (95% CI: 0, 0.16) and 0.16 z-score (95% CI: 0.07, 0.24), respectively, but changed very little after additional adjustment for number of older siblings and mother’s smoking status. Associations were similar when based on paternal educational attainment and highest household occupation.

Conclusions

In Belarus, consistent with some middle-income countries, higher socioeconomic position was associated with greater BMI trajectories from age 3 onwards.

Estimation of the linear mixed integrated Ornstein-Uhlenbeck model

The linear mixed model with an added integrated Ornstein–Uhlenbeck (IOU) process (linear mixed IOU model) allows for serial correlation and estimation of the degree of derivative tracking. It is rarely used, partly due to the lack of available software. We implemented the linear mixed IOU model in Stata and using simulations we assessed the feasibility of fitting the model by restricted maximum likelihood when applied to balanced and unbalanced data. We compared different (1) optimization algorithms, (2) parameterizations of the IOU process, (3) data structures and (4) random-effects structures. Fitting the model was practical and feasible when applied to large and moderately sized balanced datasets (20,000 and 500 observations), and large unbalanced datasets with (non-informative) dropout and intermittent missingness. Analysis of a real dataset showed that the linear mixed IOU model was a better fit to the data than the standard linear mixed model (i.e. independent within-subject errors with constant variance).

Comparison of imputation variance estimators

Appropriate imputation inference requires both an unbiased imputation estimator and an unbiased variance estimator. The commonly used variance estimator, proposed by Rubin, can be biased when the imputation and analysis models are misspecified and/or incompatible. Robins and Wang proposed an alternative approach, which allows for such misspecification and incompatibility, but it is considerably more complex. It is unknown whether in practice Robins and Wang's multiple imputation procedure is an improvement over Rubin's multiple imputation. We conducted a critical review of these two multiple imputation approaches, a re-sampling method called full mechanism bootstrapping and our modified Rubin's multiple imputation procedure via simulations and an application to data. We explored four common scenarios of misspecification and incompatibility. In general, for a moderate sample size (n = 1000), Robins and Wang's multiple imputation produced the narrowest confidence intervals, with acceptable coverage. For a small sample size (n = 100) Rubin's multiple imputation, overall, outperformed the other methods. Full mechanism bootstrapping was inefficient relative to the other methods and required modelling of the missing data mechanism under the missing at random assumption. Our proposed modification showed an improvement over Rubin's multiple imputation in the presence of misspecification. Overall, Rubin's multiple imputation variance estimator can fail in the presence of incompatibility and/or misspecification. For unavoidable incompatibility and/or misspecification, Robins and Wang's multiple imputation could provide more robust inferences.

Relative efficiency of joint-model and full-conditional-specification multiple imputation when conditional models are compatible: The general location model

Estimating the parameters of a regression model of interest is complicated by missing data on the variables in that model. Multiple imputation is commonly used to handle these missing data. Joint model multiple imputation and full-conditional specification multiple imputation are known to yield imputed data with the same asymptotic distribution when the conditional models of full-conditional specification are compatible with that joint model. We show that this asymptotic equivalence of imputation distributions does not imply that joint model multiple imputation and full-conditional specification multiple imputation will also yield asymptotically equally efficient inference about the parameters of the model of interest, nor that they will be equally robust to misspecification of the joint model. When the conditional models used by full-conditional specification multiple imputation are linear, logistic and multinomial regressions, these are compatible with a restricted general location joint model. We show that multiple imputation using the restricted general location joint model can be substantially more asymptotically efficient than full-conditional specification multiple imputation, but this typically requires very strong associations between variables. When associations are weaker, the efficiency gain is small. Moreover, full-conditional specification multiple imputation is shown to be potentially much more robust than joint model multiple imputation using the restricted general location model to mispecification of that model when there is substantial missingness in the outcome variable.

Transformation of truncated gold octahedrons into triangular nanoprisms through the heterogeneous nucleation of silver

Described is a straightforward procedure for forming organized substrate-immobilized nanoprisms which are single crystalline, surfactant-free and which form a heteroepitaxial relationship with the underlying substrate. The devised route utilizes truncated Au octahedrons formed through solid state dewetting techniques as high temperature heterogeneous nucleation sites for Ag adatoms which are arriving to the substrate surface in the vapour phase. Observed is a morphological and compositional transformation of the Au structures to triangular nanoprisms comprised of a homogeneous AuAg alloy. During this transformation, the localized surface plasmon resonance red-shifts, broadens and increases in strength. The shape transformation, which cannot be rationalized using thermodynamic arguments dependent on the surface energy minimization, is described in terms of a kinetically driven growth mode, previously predicted by molecular dynamic simulations. The so-formed structures, when coated with a thin layer of Pd, are demonstrated as plasmonic sensing elements for hydrogen detection.

Maternal and childhood psychological factors predict chronic disabling fatigue at age 13 years

PURPOSE

To investigate whether premorbid maternal and childhood psychological problems are risk factors for chronic disabling fatigue at age 13 years among children in the Avon Longitudinal Study of Parents and Children birth cohort.

METHODS

Chronic disabling fatigue was defined as fatigue of at least 3-month, and up to 5-year, duration that prevented school attendance or hobbies/sport/leisure activities, and for which other causes were not identified. Maternal psychological factors were symptoms of anxiety and depression assessed up to eight times between pregnancy and age 6 years. We investigated critical periods for maternal effects and effects of paternal depression at three time points. Child psychological factors included internalizing and externalizing problems and upsetting life events occurring at age 7-8 years.

RESULTS

Of 5,657 children, 110 (1.9%) had chronic disabling fatigue at age 13 years. Maternal anxiety (adjusted odds ratio [AOR], 1.19; 95% confidence interval [CI], 1.09-1.31 per episode), maternal depression (AOR, 1.24; CI, 1.11-1.39 per episode), child psychological problems (AOR, 1.19; CI, 1.00-1.41 per problem), and upsetting events (AOR, 1.22; CI, .99-1.58 per event) were associated with chronic disabling fatigue. Associations of child psychological problems and upsetting events were attenuated (AOR, 1.12; CI, .93-1.33 per problem; AOR, 1.19; CI, .94-1.52 per event) after further adjusting for maternal anxiety and depression.

CONCLUSIONS

Pediatricians need to be aware that children whose mothers experience anxiety and/or depression between pregnancy and child's age 6 years have an increased risk of developing chronic disabling fatigue in early adolescence. Conversely, clinicians need to be alert to fatigue in children whose mothers have longstanding anxiety and depression. These findings suggest the importance of family-based approaches to treatment.

Modelling childhood growth using fractional polynomials and linear splines

BACKGROUND

There is increasing emphasis in medical research on modelling growth across the life course and identifying factors associated with growth. Here, we demonstrate multilevel models for childhood growth either as a smooth function (using fractional polynomials) or a set of connected linear phases (using linear splines).

METHODS

We related parental social class to height from birth to 10 years of age in 5,588 girls from the Avon Longitudinal Study of Parents and Children (ALSPAC). Multilevel fractional polynomial modelling identified the best-fitting model as being of degree 2 with powers of the square root of age, and the square root of age multiplied by the log of age. The multilevel linear spline model identified knot points at 3, 12 and 36 months of age.

RESULTS

Both the fractional polynomial and linear spline models show an initially fast rate of growth, which slowed over time. Both models also showed that there was a disparity in length between manual and non-manual social class infants at birth, which decreased in magnitude until approximately 1 year of age and then increased.

CONCLUSIONS

Multilevel fractional polynomials give a more realistic smooth function, and linear spline models are easily interpretable. Each can be used to summarise individual growth trajectories and their relationships with individual-level exposures.

Joint modelling rationale for chained equations

Background

Chained equations imputation is widely used in medical research. It uses a set of conditional models, so is more flexible than joint modelling imputation for the imputation of different types of variables (e.g. binary, ordinal or unordered categorical). However, chained equations imputation does not correspond to drawing from a joint distribution when the conditional models are incompatible. Concurrently with our work, other authors have shown the equivalence of the two imputation methods in finite samples.

Methods

Taking a different approach, we prove, in finite samples, sufficient conditions for chained equations and joint modelling to yield imputations from the same predictive distribution. Further, we apply this proof in four specific cases and conduct a simulation study which explores the consequences when the conditional models are compatible but the conditions otherwise are not satisfied.

Results

We provide an additional “non-informative margins” condition which, together with compatibility, is sufficient. We show that the non-informative margins condition is not satisfied, despite compatible conditional models, in a situation as simple as two continuous variables and one binary variable. Our simulation study demonstrates that as a consequence of this violation order effects can occur; that is, systematic differences depending upon the ordering of the variables in the chained equations algorithm. However, the order effects appear to be small, especially when associations between variables are weak.

Conclusions

Since chained equations is typically used in medical research for datasets with different types of variables, researchers must be aware that order effects are likely to be ubiquitous, but our results suggest they may be small enough to be negligible.

Effect of pig breed and dietary protein level on selected fatty acids and stearoyl-coenzyme A desaturase protein expression in longissimus muscle and subcutaneous fat

The aims of the study were 1) to investigate effects of a low protein diet on fatty acids content and composition of the LM and subcutaneous adipose tissue in 3 genetically diverse breeds, Large White × Landrace, Alentejano, and Bizaro, and 2) to determine whether the effect of the low protein diet of fatty acid composition is associated with dietary modulation of stearoyl-CoA desaturase (SCD) protein expression. The experiments were conducted on 12 Large White × Landrace, 12 Alentejano, and 10 Bízaro female and male pigs. The average animal BW at the beginning of experiments was 40.8, 40.7, and 38.3 kg for Large White × Landrace, Alentejano, and Bízaro, respectively, and the BW of animals at slaughter was 90 kg. The diets contained 202 or 169 g/kg DM of CP (high and low protein diets, respectively) and were balanced in essential AA. The diets were fed until the animals reached 90 kg BW (approximately 73 d). It was established that Large White × Landrace pigs had a less (P = 0.001) total fatty acid content in subcutaneous adipose tissue when compared with Alentejano and Bízaro and less (P < 0.001) intramuscular fat (IMF) content when compared with Alentejano. There was a positive relationship between SCD protein expression in the LM and MUFA content (r = 0.627, P = 0.029) and SCD protein expression and total muscle fatty acids content (r = 0.725, P = 0.008) in Large White × Landrace but not in Alentejano and Bizaro breeds. It has been suggested that SCD protein expression is associated with regulation of fat deposition only in breeds with genetic predisposition to a low IMF content.

Altering the dewetting characteristics of ultrathin gold and silver films using a sacrificial antimony layer

Solid state dewetting of ultrathin films is the most straightforward means of fabricating substrate-supported noble metal nanostructures. This assembly process is, however, quite inflexible, yielding either densely packed smaller structures or widely spaced larger structures. Here, we demonstrate the utility of introducing a sacrificial antimony layer between the substrate and noble metal overlayer. We observe an agglomeration process which is radically altered by the concurrent sublimation of antimony. In stark contrast with conventional dewetting, where the thickness of the deposited metal film determines the characteristic length scales of the assembly process, it is the thickness of the sacrificial antimony layer which dictates both the nanoparticle size and interparticle spacing. The result is a far more flexible self-assembly process where the nanoparticle size and areal density can be varied widely. Demonstrations show nanoparticle areal densities which are varied over four orders of magnitude assembled from the identical gold layer thickness, where the accompanying changes to nanostructure size see a systematic shift in the wavelength of the localized surface plasmon resonance. As a pliable self-assembly process, it offers the opportunity to tailor the properties of an ensemble of nanostructures to meet the needs of specific applications.

[Guillain-Barré syndrome after exposure to influenza]

Guillain-Barré Syndrome (GBS) is an acquired, monophasic inflammatory polyradiculoneuritis of autoimmune origin, which occurs after infection and occasionally also after vaccination. Seasonal and pandemic influenza vaccines have in particular been implicated as triggers for GBS. However, a number of recent studies indicate that infection with influenza virus may also cause GBS. This review summarizes the epidemiological and experimental data of the association of GBS with exposure to influenza antigens by immunization (including vaccines against A/H1N1/2009) and infection. Vaccination against influenza is associated with a very low risk for the occurrence of GBS. In contrast infection with influenza may play a more important role as a triggering factor for GBS than previously assumed.

Reducing smoking in adolescents: cost-effectiveness results from the cluster randomized ASSIST (A Stop Smoking In Schools Trial)

Introduction:

School-based smoking prevention programmes can be effective, but evidence on cost-effectiveness is lacking. We conducted a cost-effectiveness analysis of a school-based “peer-led” intervention.

Methods:

We evaluated the ASSIST (A Stop Smoking In Schools Trial) programme in a cluster randomized controlled trial. The ASSIST programme trained students to act as peer supporters during informal interactions to encourage their peers not to smoke. Fifty-nine secondary schools in England and Wales were randomized to receive the ASSIST programme or usual smoking education. Ten thousand seven hundred and thirty students aged 12–13 years attended participating schools. Previous work has demonstrated that the ASSIST programme achieved a 2.1% (95% CI = 0%–4.2%) reduction in smoking prevalence. We evaluated the public sector cost, prevalence of weekly smoking, and cost per additional student not smoking at 24 months.

Results:

The ASSIST programme cost of £32 (95% CI = £29.70–£33.80) per student. The incremental cost per student not smoking at 2 years was £1,500 (95% CI = £669–£9,947). Students in intervention schools were less likely to believe that they would be a smoker at age 16 years (odds ratio [OR] = 0.80; 95% CI = 0.66–0.96).

Conclusions:

A peer-led intervention reduced smoking among adolescents at a modest cost. The intervention is cost-effective under realistic assumptions regarding the extent to which reductions in adolescent smoking lead to lower smoking prevalence and/or earlier smoking cessation in adulthood. The annual cost of extending the intervention to Year 8 students in all U.K. schools would be in the region of £38 million and could result in 20,400 fewer adolescent smokers.

The role of substrate surface alteration in the fabrication of vertically aligned CdTe nanowires

Previously we have described the deposition of vertically aligned wurtzite CdTe nanowires derived from an unusual catalytically driven growth mode. This growth mode could only proceed when the surface of the substrate was corrupted with an alcohol layer, although the role of the corruption was not fully understood. Here, we present a study detailing the remarkable role that this substrate surface alteration plays in the development of CdTe nanowires; it dramatically improves the size uniformity and largely eliminates lateral growth. These effects are demonstrated to arise from the altered surface's ability to limit Ostwald ripening of the catalytic seed material and by providing a surface unable to promote the epitaxial relationship needed to sustain a lateral growth mode. The axial growth of the CdTe nanowires is found to be exclusively driven through the direct impingement of adatoms onto the catalytic seeds leading to a self-limiting wire height associated with the sublimation of material from the sidewall facets. The work presented furthers the development of the mechanisms needed to promote high quality substrate-based vertically aligned CdTe nanowires. With our present understanding of the growth mechanism being a combination of selective area epitaxy and a catalytically driven vapour-liquid-solid growth mode, these results also raise the intriguing possibility of employing this growth mode in other material systems in an effort to produce superior nanowires.

From Amino Acids to Heteroaromatics—Thiopeptide Antibiotics, Nature's Heterocyclic Peptides

Amino acids, the building blocks of proteins, also serve as precursors to a wide range of other naturally occurring substances including alkaloids, antibiotics, and, the subject of this Review, heterocyclic peptides. Simple alpha-amino acids are converted into complex arrays of heteroaromatic rings that display interesting and potent biological activity. The thiopeptide antibiotics, with their complex molecular architectures, are wonderful examples. In this Review we show how organic chemists have developed innovative methods for the synthesis of the heterocyclic ring systems, including routes inspired by the likely biosynthetic processes, and successfully assembled such building blocks into the final target molecule by application of orthogonal protecting groups and coupling methodologies.

Endoneurial injection of antisera to myelin antigens

When antisera to purified myelin antigens were injected into rat sciatic nerves, some produced significant demyelination, whereas others merely induced an inflammatory infiltrate. Extensive demyelination was produced by antisera to galactocerebroside and the peripheral nerve glycoprotein P0. Demyelination resulting from injections of antisera to ganglioside GM1, P2, myelin basic protein, sulfatide, and glucocerebroside did not exceed that produced by normal rabbit serum. Addition of guinea pig complement had no effect. It is of interest that the greatest demyelination followed injection of antisera to two molecules, galactocerebroside and P0, the main antigenic determinants of which present at the Schwann cell surface.

Current Strategies for Modulating Lymphangiogenesis Signalling Pathways in Human Disease

The recent discovery that members of the vascular endothelial growth factor (VEGF) family of secreted glycoproteins can mediate lymphatic vessel growth (lymphangiogenesis) via cell surface receptor tyrosine kinases expressed on endothelial cells has opened the way for therapeutic intervention for pathologies involving dysregulated lymphatic vessel function. At least two members of this family, VEGF-C and VEGF-D, have been shown to induce lymphangiogenesis in vivo. Lymphatic vessels and their specific growth factors have been directly implicated in a number of significant human pathologies. In cancer, VEGF-C and VEGF-D appear to correlate with tumor metastasis and poor patient outcome in a range of prevalent human cancers. Experimental studies have demonstrated that expression of the lymphangiogenic growth factors in tumor models induces increased lymphangiogenesis and results in spread of tumor cells via the lymphatics. In contrast, conditions such as lymphedema, where lymphatic vessels fail to clear fluid from interstitial spaces, are opportunities for which the application of growth factors to generate new lymphatic vessels may be a viable therapeutic option. The list of molecules that control lymphangiogenesis is now expanding, allowing more opportunities for the development of drugs with which to manipulate the relevant signalling pathways. Modulating these pathways and other molecules with specificity to the lymphatic endothelium could offer alternative treatments for a number of important clinical conditions.

Total synthesis of the thiopeptide antibiotic amythiamicin D

The thiopeptide (or thiostrepton) antibiotics are a class of sulfur containing highly modified cyclic peptides with interesting biological properties, including reported activity against MRSA and malaria. Described herein is the total synthesis of the thiopeptide natural product amythiamicin D, which utilizes a biosynthesis-inspired hetero-Diels-Alder route to the pyridine core of the antibiotic as a key step. Preliminary studies using a range of serine-derived 1-ethoxy-2-azadienes established that hetero-Diels-Alder reaction with N-acetylenamines proceeded efficiently under microwave irradiation to give 2,3,6-trisubstituted pyridines. The thiazole building blocks of the antibiotic were obtained by either classical Hantzsch reactions or by dirhodium(II)-catalyzed chemoselective carbene N-H insertion followed by thionation, and were combined to give the bis-thiazole that forms the left-hand fragment of the antibiotic. The key Diels-Alder reaction of a tris-thiazolyl azadiene with benzyl 2-(1-acetylaminoethenyl)thiazole-4-carboxylate gave the core tetrathiazolyl pyridine, which was elaborated into the natural product by successive incorporation of glycine and bis-thiazole fragments followed by macrocyclization.

Solution structures of thiopeptide antibiotics

A detailed NMR study of the thiopeptide amythiamicin D establishes its solution conformation and the presence of a single intramolecular hydrogen bond involving NH13 and O28, and also provides the first evidence for self-association of thiopeptides in solution.

Rotational spectrum, inversion, and geometry of 2,5-dihydrofuran...ethyne and a generalization about Z...H-C hydrogen bonds

The ground-state rotational spectra of nine isotopomers of a complex formed between 2,5-dihydrofuran and ethyne were recorded with a pulsed-jet, Fourier-transform microwave spectrometer. Rotational and centrifugal distortion constants were obtained for C4H6O...HCCH, C4H6O...DCCH, C4H6O...HCCD, C4H6O...DCCD, [3,4-D2]-C4H6O...HCCH, C4H6O...H13CCH, C4H6O...HC13CH, , and [3(13C]-C4H6O...HCCH. The substituted species were studied in their natural abundances. For the more abundant isotopomers, weak c-type transitions as well as strong a-type transitions were observed. The primary intermolecular binding was shown to consist of a hydrogen bond formed by the ethyne subunit acting as the proton donor and the O atom of 2,5-dihydrofuran as the proton acceptor. The complex has a plane of symmetry that includes the O atom and the ethyne subunit, with a pyramidal configuration at oxygen. A fit of the principal moments of inertia of all nine isotopomers under the assumption of unperturbed 2,5-dihydrofuran and ethyne geometries yielded the values r(O...H)=2.127(8) A, phi=57.8(18) degrees , and theta=16.2(32) degrees, where phi is the angle made by the HCCH subunit at O and theta is the angular deviation of the O...H-C nuclei from collinearity. This geometry is compared with those obtained by ab initio calculations conducted with a range of basis sets and with electron correlation taken into account at the MP2 (Møller-Plesset second order) level of theory. A small inversion doubling (approximately equal to 20-30 kHz) of c-type transitions, well resolved only for the parent isotopomer and [3HCCH, was attributed to a vibrational motion that inverts the configuration at oxygen. A one-dimensional model for this motion was used with a double minimum potential energy function of the type V(phi)=alphaphi(4)+betaphi(2) to estimate the observed separation DeltaE(01) of the lowest pair (v=0 and v=1) of associated energy levels. The predicted DeltaE(01) had the same magnitude as that deduced from the inversion doubling of the c-type transitions. The geometry of C4H6O...HCCH is compared with those other B...HCCH, where B is vinyl fluoride, oxirane, and thiirane. A rationalization of the angular geometries of various B...HX, where X=F, Cl, Br, or CCH, is presented.

Probing the mechanism of Prins cyclisations and application to the synthesis of 4-hydroxytetrahydropyrans

Trapping intermediates on the Prins cyclisation pathway with carbon-based nucleophiles has given further insight into factors affecting the acid-mediated reactions of homoallylic alcohols with aldehydes, enabling the design of efficient syntheses of 4-hydroxy-2,6-disubstituted tetrahydropyrans.

Molecular targeting of lymphatics for therapy

The dysfunction or proliferation of lymphatic vessels (lymphangiogenesis) is linked to a number of pathological conditions including lymphedema and cancer. The recent discovery and characterisation of the lymphangiogenic growth factors vascular endothelial growth factor-C (VEGF-C) and VEGF-D and of their receptor on lymphatic endothelial cells, VEGFR-3, has provided an understanding of the molecular mechanisms controlling the growth of lymphatic vessels. In addition, other genes and protein markers have been identified with specificity for lymphatic endothelium that have enhanced the characterization and isolation of lymphatic endothelial cells. Our growing understanding of the molecules that control lymphangiogenesis allows us to design more specific drugs with which to manipulate the relevant signalling pathways. Modulating these pathways and other molecules with specificity to the lymphatic system could offer alternative treatments for a number of important clinical conditions.

Total synthesis of the thiopeptide amythiamicin D

The first total synthesis of the thiopeptide antibiotic amythiamicin D is described.

Folate supplementation and methotrexate treatment in rheumatoid arthritis: a review

OBJECTIVES

The folate antagonist methotrexate (MTX) has become established as the most commonly used disease-modifying anti-rheumatic drug (DMARD) in the treatment of rheumatoid arthritis (RA) but is commonly discontinued due to adverse effects. Adverse effects are thought to be mediated via folate antagonism. In this paper we summarize the current data on the use of folates as a supplement to MTX use in RA for the prevention of adverse effects and as a potential modulator of cardiovascular risk, and propose guidelines for standard practice.

METHODS

A Medline search was performed using the search terms "methotrexate", "folic acid", "folinic acid", "folate" and "homocysteine". Literature relevant to the use of folates as a supplement to MTX in the treatment of RA was reviewed and other papers referred to as references were explored.

RESULTS

The use of supplemental folates, including folic and folinic acid, in RA patients treated with MTX has been shown to improve continuation rates by reducing the incidence of liver function test abnormalities and gastrointestinal intolerance. Folate supplements do not appear to significantly reduce the effectiveness of MTX in the treatment of RA. Furthermore, supplemental folic acid offsets the elevation in plasma homocysteine associated with the use of MTX. This may in turn reduce the risk of cardiovascular disease, which is over-represented amongst patients with RA, and for which hyperhomocysteinaemia is now recognized as an independent risk factor.

CONCLUSIONS

We propose that folic acid supplements be prescribed routinely to all patients receiving MTX for the treatment of RA. We recommend a pragmatic dosing schedule of 5 mg of oral folic acid given on the morning following the day of MTX administration.

Stereoselective synthesis of 4-hydroxy-2,3,6-trisubstituted tetrahydropyrans

[reaction: see text] Reaction of homoallylic alcohols with aldehydes in the presence of TFA gives, after hydrolysis of the ester, 4-hydroxy-2,3,6-trisubstituted tetrahydropyrans with the creation of three new stereocenters in a single-pot process. By varying the aldehyde component, a variety of functionalized side chains are installed at C-2. The utility of this approach is extended to the enantioselective synthesis of tetrahydropyrans with >99% ee.

Cytotoxic drugs and interferons for chronic inflammatory demyelinating polyradiculoneuropathy

BACKGROUND

Chronic inflammatory demyelinating polyradiculoneuropathy is a disease causing progressive or relapsing and remitting weakness and numbness. It is probably due to an autoimmune inflammatory process. Immunosuppressive or immunomodulatory drugs would be expected to be beneficial.

OBJECTIVES

We aimed to review systematically the evidence from randomised trials concerning cytotoxic drugs and interferons for chronic inflammatory demyelinating polyradiculoneuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (searched December 2001), MEDLINE (searched January 1977 to December 2001), EMBASE (January 1980 to December 2001), CINAHL (searched January 1982 to December 2001) and LILACS (searched January 1982 to December 2001). We contacted the authors of the trials identified and other disease experts seeking other published and unpublished trials.

SELECTION CRITERIA

We sought randomised and quasi-randomised trials of all immunosuppressive agents such as azathioprine, cyclophosphamide, methotrexate, cyclosporin A, mycophenolate mofetil, and rituximab and all immunomodulatory agents such as alpha interferon and beta interferon in participants fulfilling standard diagnostic criteria for chronic inflammatory demyelinating polyradiculoneuropathy.

DATA COLLECTION AND ANALYSIS

Two of us independently selected the trials which met our criteria, judged their methodological quality and extracted the data onto specially designed forms. We wanted to measure the change in disability after one year as our primary outcome measure.

MAIN RESULTS

We found one parallel group open trial of azathioprine for nine months involving 27 participants and another of interferon beta involving 10 participants in a double blind crossover trial with each treatment period lasting 12 weeks. Neither trial provided our primary outcome measure and neither showed a significant beneficial effect on any of the outcome measures selected by the authors or ourselves in the protocol for this review.

REVIEWER'S CONCLUSIONS

The evidence is inadequate to decide whether azathioprine, interferon beta or any other immunosuppressive drug or interferon is beneficial in chronic inflammatory demyelinating polyradiculoneuropathy.

Biosynthesis inspired Diels-Alder route to pyridines: synthesis of the 2,3-dithiazolylpyridine core of the thiopeptide antibiotics

Reaction of serine derived 1-alkoxy-2-azadienes with dehydroalanine derived dienophiles results in Diels-Alder reaction and aromatisation to give 2,3,6-trisubstituted pyridines, thereby establishing the viability of the proposed biosynthetic route to the pyridine ring of the thiopeptide antibiotics originally proposed by Bycroft and Gowland.

Review of the function of a telephone helpline in the treatment of outpatients with rheumatoid arthritis

OBJECTIVES

To examine the role, acceptability, and cost effectiveness of a telephone helpline organised and run by specialist nurses in a district general hospital outpatient rheumatology department.

MATERIAL AND METHODS

Patients accessed the telephone helpline by leaving a taped message on an answer phone with a 24 hour response time. Assessment included an audit of the nature and outcome of helpline calls, patient satisfaction with the helpline, and a health economic analysis of the helpline operation. A postal questionnaire was used to assess patient satisfaction; this was sent to the 87 patients who called the helpline during one month, and overall satisfaction with the helpline was assessed. The nature and outcome of all calls was analysed retrospectively using a helpline record book for February and October of one year and February of the following year. From the results of the retrospective analysis and an estimate of the number of general practitioner consultations avoided by provision of the helpline, the cost effectiveness of the helpline was calculated.

RESULTS

Of those returning questionnaires, 61/63 (97%) were satisfied with the response time, 63/63 (100%) with the courtesy, and 60/63 (95%) felt that their questions were answered directly and to their satisfaction in 62 (98%) of cases. Had the helpline not been available, 38/63 (60%) patients would have made an appointment with their GP. When these figures were extrapolated to an annual estimation, a basic cost analysis showed that the helpline produced a cost saving to the NHS, largely as a result of GP consultations avoided.

CONCLUSION

Clinical advice and support can be provided by a rheumatology helpline set up as an adjunct to a standard outpatient service. The results of a postal questionnaire suggested more than 95% satisfaction with all aspects of the helpline service and that 99% of callers would call the helpline again. The provision of the helpline service contributes to the quality of care provided by an outpatient department and provides benefit to the NHS.

Corticosteroids for chronic inflammatory demyelinating polyradiculoneuropathy

BACKGROUND

Chronic inflammatory demyelinating polyradiculoneuropathy is a peripheral neuropathy caused by peripheral nerve inflammation probably due to autoimmunity and would be expected to benefit from corticosteroids. Non-randomised studies suggest that corticosteroids are often beneficial.

OBJECTIVES

To evaluate the efficacy of corticosteroids for treating chronic inflammatory demyelinating polyradiculoneuropathy.

SEARCH STRATEGY

Search of the Cochrane Neuromuscular Disease Group register for randomised trials of corticosteroids treatment for chronic inflammatory demyelinating polyradiculoneuropathy and enquiry from subject experts.

SELECTION CRITERIA

Types of studies: All randomised or quasi-randomised trials Types of Participants: All patients with chronic inflammatory demyelinating polyradiculoneuropathy who were diagnosed by an internationally accepted definition. Types of interventions: Treatment with any form of corticosteroids or adrenocorticotropic hormone. Types of outcome measures:

PRIMARY OUTCOME MEASURE

Change in disability 12 weeks after randomisation.

SECONDARY OUTCOME MEASURES

1. Change in impairment 12 weeks after randomisation. 2. Change in maximum motor nerve conduction velocity or compound muscle action potential amplitude after 12 weeks. 3. Side effects of corticosteroids.

DATA COLLECTION AND ANALYSIS

One author extracted the data and the other checked them.

MAIN RESULTS

We identified one randomised controlled trial, an open study in which 19 corticosteroids treated patients showed more improvement in impairment than 16 untreated controls after 12 weeks. Experience from large non-randomised studies suggests that steroids are beneficial.

REVIEWER'S CONCLUSIONS

A single randomised controlled trial with 35 participants provided weak evidence to support the conclusion from non-randomised studies that oral corticosteroids reduce impairment in chronic inflammatory demyelinating polyradiculoneuropathy. Corticosteroids are known to have serious long term side effects. The long term risk and benefits have not been adequately studied.

Plasma exchange for Guillain-Barré syndrome

BACKGROUND

Guillain-Barré syndrome is an acute symmetric, usually ascending and usually paralysing illness, due to inflammation of peripheral nerves. It is thought to be caused by autoimmune factors, such as antibodies. Plasma exchange removes antibodies and other potentially injurious factors from the blood stream. It involves connecting the patient's blood circulation to a machine which exchanges the plasma for a substitute solution, usually albumin. Several studies have evaluated plasma exchange for Guillain-Barré syndrome.

OBJECTIVES

To systematically review the evidence concerning the efficacy of plasma exchange for treating Guillain-Barré syndrome.

SEARCH STRATEGY

Search of the Cochrane Neuromuscular Disease Trial Register for randomised trials concerning plasma exchange in Guillain-Barré syndrome, search of the bibliographies of identified papers and enquiry from the authors of the papers.

SELECTION CRITERIA

Randomised and quasi-randomised trials of plasma exchange versus sham exchange or supportive treatment.

DATA COLLECTION AND ANALYSIS

Potentially relevant papers were scrutinised by two reviewers and the selection of eligible studies was agreed by them and a third reviewer. Data were extracted by one reviewer and checked by a second reviewer. Some missing data were obtained from the authors of studies.

MAIN RESULTS

Six eligible trials concerning 649 patients were identified, all comparing plasma exchange versus supportive treatment alone. Primary outcome measures ~bullet~Time to recover walking with aid In the only two trials for which this measure was reported, the median time to recover this ability was faster in the plasma exchange than the control group. ~bullet~Time to onset of motor recovery in mildly affected patients In the one trial for which this measure was available, the time was significantly shortened in the plasma exchange group. Secondary outcome measures ~bullet~Improvement in disability grade at four weeks In five trials, there were significantly more patients who had improved by one disability grade or more in the plasma exchange group as compared to the control group. Patients treated with plasma exchange fared significantly better in the following secondary outcome measures: time to recover walking without aid, percentage of patients requiring artificial ventilation, duration of ventilation, full muscle strength recovery after one year, and severe sequelae after one year. There were less patients with infectious events and cardiac arrhythmias in the plasma exchange than the control group. Subgroup analyses Plasma exchange was beneficial in patients with mild, moderate and severe (needing ventilation) Guillain-Barré syndrome. It was beneficial in patients with a disease duration of seven or less days and also in those with disease lasting more than seven days. However, in the only trial that enrolled patients up to 30 days from disease onset, the benefit of plasma exchange in patients treated after seven days was less apparent. Type of treatment Single studies showed that two plasma exchanges were significantly superior to none for mild Guillain-Barré syndrome and four to two for moderate Guillain-Barré syndrome, but that six were not superior to four for severe Guillain-Barré syndrome requiring ventilation. One study suggested that continuous flow plasma exchange was significantly superior to intermittent flow. Another study found no significant difference between the two techniques. The same study found a significantly higher rate of adverse events with fresh frozen plasma as the replacement fluid than albumin. Plasma exchange compared with cerebrospinal fluid filtration A single trial comparing these two treatments did not show any difference in outcomes but was too small to demonstrate equivalence.

REVIEWER'S CONCLUSIONS

Plasma exchange is the first and only treatment that has been proven to be superior to supportive treatment alone in Guillain-Barré syndrome. Consequently, plasma exchange should be regarded as the treatment against which new treatments, such as intravenous immunoglobulin, should be judged. In mild Guillain-Barré syndrome two sessions of plasma exchange are superior to none. In moderate Guillain-Barré syndrome four sessions are superior to two. In severe Guillain-Barré syndrome six sessions are no better than four. Continuous flow plasma exchange machines may be superior to intermittent flow machines and albumin to fresh frozen plasma as the exchange fluid. Plasma exchange is more beneficial when started within seven days after disease onset rather than later, but was still beneficial in patients treated up to 30 days after disease onset. The value of plasma exchange in children less than 12 years old is not known. There is insufficient evidence to determine whether cerebrospinal fluid filtration is equivalent to plasma exchange.

Immunosuppressive treatment for multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy is a distinct clinical entity characterised by progressive, predominantly distal, asymmetrical limb weakness and minimal sensory abnormality. The pathognomonic feature of this condition is the presence of multiple partial motor nerve conduction blocks. Controlled trials have demonstrated the efficacy of regular intravenous immunoglobulin infusions. Immunosuppressive agents have been used as primary, second-line or adjunctive agents for its treatment. This review was undertaken to identify and review systematically randomised controlled trials of immunosuppressive agents. The use of intravenous immunoglobulin will be the subject of a separate review.

OBJECTIVES

To provide the best available evidence from randomised controlled trials on the role of immunosuppressive agents for the treatment of multifocal motor neuropathy.

SEARCH STRATEGY

The Cochrane Neuromuscular Disease Group register was searched for all trials of multifocal motor neuropathy published, using 'multifocal motor neuropathy' OR 'chronic inflammatory demyelinating polyradiculoneuropathy' OR ' conduction block' OR ' motor neuropathy' AND 'immunosuppressive agents', 'immunosuppressants', 'corticosteroids', 'plasma exchange', 'azathioprine', 'cyclophosphamide', 'cyclosporin', 'methotrexate', and 'mycophenolate', 'immunomodulatory agents', 'interferon', 'total lymphoid irradiation' or 'bone marrow transplantation' as search terms. In addition we searched MEDLINE, EMBASE for 2000 and 2001 and CINAHL, LILACS for all years.

SELECTION CRITERIA

All randomised controlled trials and quasi-randomised clinical trials in which allocation was not random but was intended to be unbiased (e.g. alternate allocation) were to have been selected. Since no such trials were discovered, all prospective and retrospective case series were included in 'background' or 'discussion' sections of the review.

DATA COLLECTION AND ANALYSIS

All studies on multifocal motor neuropathy or lower motor neuron weakness with conduction block and no sensory abnormality were scrutinized for data on patients treated with any form of immunosuppressive agents besides intravenous immunoglobulin. The information on the outcome of treatment was then collated and summarised.

MAIN RESULTS

We found no randomised controlled trials of any immunosuppressive agents for multifocal motor neuropathy. We summarised the results of retrospective and prospective case series in the discussion of the review.

REVIEWER'S CONCLUSIONS

There are no randomised controlled trials to indicate whether immunosuppressive agents are beneficial in multifocal motor neuropathy.