Familial progressive supranuclear palsy: detection of subclinical cases using 18F-dopa and 18fluorodeoxyglucose positron emission tomography

Intrastriatal gradient analyses of 18F-FDOPA PET scans for differentiation of Parkinsonian disorders

•

FDOPA PET allows quantification of presynaptic dopaminergic functioning in vivo.

•

Subregional analysis within the striatum provides additional diagnostic value for differentiation within Parkinsonian disorders.

•

Depletion of F-DOPA uptake in both patients with idiopathic Parkinson's disease and patients with atypical Parkinsonism preferentially affects the posterior part of the putamen.

•

A more linear decrease of FDOPA uptake from the head of the caudate nucleus to the posterior putamen is present in patients with IPD than in APD.

Aim

L -3,4-dihydroxy-6–18F-fluorophenylalanine (18F-DOPA PET may be used to distinguish subjects with Parkinsonism from those with symptoms not originating from impaired dopaminergic transmission. However, it is not routinely utilized to discriminate Idiopathic Parkinson's disease (IPD) from Atypical Parkinsonian Disorders (APD). We investigated the potential of FDOPA PET to discriminate between IPD and APD, with a focus on the anterior-to-posterior decline in het striatum, considered to be more specific for IPD.

Materials and methods

18F-DOPA PET data from a total of 58 subjects were retrospectively analyzed. 28 subjects had idiopathic Parkinson's disease (14 male, 14 female; age at scan 61 +- 11,5), 13 atypical Parkinsonian disease (7 male, 6 females; age at scan: 69,6 +- 6,4) and 17 were controls (6 male, 11 female; age at scan 65,3 +-8,6). Regional striatal-to-occipital ratio's (RSOR's) were calculated, as well as multiple in-line VOI's from the caudate nucleus to the posterior part of the putamen. The linearity of anteroposterior decline was determined by a linear regression fit and associated R squared values. ROC curves were calculated to assess the diagnostic performance of these measurements. Data contralateral to the clinically most affected side were used for analysis.

Results

ROC curve analysis for differentiation between controls and Parkinsonism patients showed the highest AUC for the caudate nucleus-to-posterior putamen ratio (AUC = 0.930; p < 0.00) and for the R squared value for the linear regression fit (AUC = 0.948; p = 0.006). For discrimating IPD from APD, the highest AUC was found for the caudate nucleus-to-anterior putamen ratio (0.824; p < 0.001)

Conclusions

Subregional analysis of the striatum in F-DOPA PET scans may provide additional diagnostic information in patients screened for a  presynaptic dopaminergic deficit. A more linear decrease from the head of the caudate nucleus to the posterior putamen was  present in patients with IPD, although this feature did not have additional diagnostic value over the RSOR analysis.

Midbrain atrophy in patients with presymptomatic progressive supranuclear palsy-Richardson's syndrome

INTRODUCTION

In the present study, midbrain atrophy and the pons-to-midbrain area ratio (P/M ratio) were investigated as diagnostic markers for presymptomatic progressive supranuclear palsy-Richardson's syndrome (Pre-PSP-RS).

METHODS

The present study included 27 patients with probable PSP-RS who underwent brain MRI at least twice before and after the development of clinical symptoms, age- and sex-matched participants with Parkinson's disease (PD, n = 27), and healthy controls (n = 27). The midbrain area, pons area, and P/M ratio of the Pre-PSP-RS, PD, and control subjects were measured using midsagittal images from brain MRI, and the parameters were compared among the groups.

RESULTS

The midbrain area decreased and the P/M ratio increased significantly in the Pre-PSP-RS patients compared with both the PD and control subjects (midbrain, Pre-PSP-RS vs. PD = 1.01 cm²vs. 1.29 cm², p < 0.001, Pre-PSP-RS vs. controls = 1.01 cm²vs. 1.29 cm², p < 0.001; P/M ratio, Pre-PSP-RS vs. PD = 5.27 vs. 4.03, p < 0.001, Pre-PSP-RS vs. controls = 5.27 cm²vs. 4.06 cm², p < 0.001). The P/M ratio had high sensitivity (vs. PD, 96.3%, vs. control, 88.9%) and specificity (vs. PD, 81.5%, vs. control, 96.3%) in differentiating Pre-PSP-RS patients from PD and control subjects.

CONCLUSION

Midbrain atrophy precedes the clinical symptoms of PSP-RS and could be a useful diagnostic imaging biomarker for Pre-PSP-RS. Furthermore, this information could play an important role in the development of future treatment strategies.

Clinical utility of FDG PET in Parkinson's disease and atypical parkinsonism associated with dementia

Purpose

There are no comprehensive guidelines for the use of FDG PET in the following three clinical scenarios: (1) diagnostic work-up of patients with idiopathic Parkinson’s disease (PD) at risk of future cognitive decline, (2) discriminating idiopathic PD from progressive supranuclear palsy, and (3) identifying the underlying neuropathology in corticobasal syndrome.

Methods

We therefore performed three literature searches and evaluated the selected studies for quality of design, risk of bias, inconsistency, imprecision, indirectness and effect size. Critical outcomes were the sensitivity, specificity, accuracy, positive/negative predictive value, area under the receiving operating characteristic curve, and positive/negative likelihood ratio of FDG PET in detecting the target condition. Using the Delphi method, a panel of seven experts voted for or against the use of FDG PET based on published evidence and expert opinion.

Results

Of 91 studies selected from the three literature searches, only four included an adequate quantitative assessment of the performance of FDG PET. The majority of studies lacked robust methodology due to lack of critical outcomes, inadequate gold standard and no head-to-head comparison with an appropriate reference standard. The panel recommended the use of FDG PET for all three clinical scenarios based on nonquantitative evidence of clinical utility.

Conclusion

Despite widespread use of FDG PET in clinical practice and extensive research, there is still very limited good quality evidence for the use of FDG PET. However, in the opinion of the majority of the panellists, FDG PET is a clinically useful imaging biomarker for idiopathic PD and atypical parkinsonism associated with dementia.

Radiological biomarkers for diagnosis in PSP: Where are we and where do we need to be?

PSP is a pathologically defined neurodegenerative tauopathy with a variety of clinical presentations including typical Richardson's syndrome and other variant PSP syndromes. A large body of neuroimaging research has been conducted over the past two decades, with many studies proposing different structural MRI and molecular PET/SPECT biomarkers for PSP. These include measures of brainstem, cortical and striatal atrophy, diffusion weighted and diffusion tensor imaging abnormalities, [18F] fluorodeoxyglucose PET hypometabolism, reductions in striatal dopamine imaging and, most recently, PET imaging with ligands that bind to tau. Our aim was to critically evaluate the degree to which structural and molecular neuroimaging metrics fulfill criteria for diagnostic biomarkers of PSP. We queried the PubMed, Cochrane, Medline, and PSYCInfo databases for original research articles published in English over the past 20 years using postmortem diagnosis or the NINDS-SPSP criteria as the diagnostic standard from 1996 to 2016. We define a five-level theoretical construct for the utility of neuroimaging biomarkers in PSP, with level 1 representing group-level findings, level 2 representing biomarkers with demonstrable individual-level diagnostic utility, level 3 representing biomarkers for early disease, level 4 representing surrogate biomarkers of PSP pathology, and level 5 representing definitive PSP biomarkers of PSP pathology. We discuss the degree to which each of the currently available biomarkers fit into this theoretical construct, consider the role of biomarkers in the diagnosis of Richardson's syndrome, variant PSP syndromes and autopsy confirmed PSP, and emphasize current shortfalls in the field. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

A systematic review of lessons learned from PET molecular imaging research in atypical parkinsonism

PURPOSE

To systematically review the previous studies and current status of positron emission tomography (PET) molecular imaging research in atypical parkinsonism.

METHODS

MEDLINE, ISI Web of Science, Cochrane Library, and Scopus electronic databases were searched for articles published until 29th March 2016 and included brain PET studies in progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and corticobasal syndrome (CBS). Only articles published in English and in peer-reviewed journals were included in this review. Case-reports, reviews, and non-human studies were excluded.

RESULTS

Seventy-seven PET studies investigating the dopaminergic system, glucose metabolism, microglial activation, hyperphosphorilated tau, opioid receptors, the cholinergic system, and GABA_A receptors in PSP, MSA, and CBS patients were included in this review. Disease-specific patterns of reduced glucose metabolism have shown higher accuracy than dopaminergic imaging techniques to distinguish between parkinsonian syndromes. Microglial activation has been found in all forms of atypical parkinsonism and reflects the known distribution of neuropathologic changes in these disorders. Opioid receptors are decreased in the striatum of PSP and MSA patients. Subcortical cholinergic dysfunction was more severe in MSA and PSP than Parkinson's disease patients although no significant changes in cortical cholinergic receptors were seen in PSP with cognitive impairment. GABA_A receptors were decreased in metabolically affected cortical and subcortical regions in PSP patients.

CONCLUSIONS

PET molecular imaging has provided valuable insight for understanding the mechanisms underlying atypical parkinsonism. Changes at a molecular level occur early in the course of these neurodegenerative diseases and PET imaging provides the means to aid differential diagnosis, monitor disease progression, identify of novel targets for pharmacotherapy, and monitor response to new treatments.

Familial progressive supranuclear palsy: a literature review

BACKGROUND

Many genes/loci associated with Parkinsonian disorders have been identified. However, the genetic causes for a number of familial forms of Parkinsonian disorders remain to be elucidated.

OBJECTIVE

It was the aim of this paper to review the familial progressive supranuclear palsy (PSP) cases without any known gene mutations published in the English literature.

METHODS

We searched the PubMed database for reports of familial PSP cases without known mutations.

RESULTS

We found 19 PSP families. The mean age at onset was approximately 60 years, and the mean disease duration was about 8 years. Parkinsonism and ophthalmoplegia were most frequently reported, and a vast majority of patients manifested with these two symptoms. Other symptoms such as falls, postural instability and pyramidal signs were also common. A small subset of patients transiently responded to L-dopa therapy.

CONCLUSION

There is an increasing number of reported familial PSP. A recently performed genome-wide association study indicated genetic factors for this condition. Furthermore, clinical, pathological and genetic investigations will open new avenues to the discovery of causative genes and new therapeutics for PSP.

Tauopathies with parkinsonism: clinical spectrum, neuropathologic basis, biological markers, and treatment options

Tauopathies with parkinsonism represent a spectrum of disease entities unified by the pathologic accumulation of hyperphosphorylated tau protein fragments within the central nervous system. These pathologic characteristics suggest shared pathogenetic pathways and possible molecular targets for disease-modifying therapeutic interventions. Natural history studies, for instance, in progressive supranuclear palsy, frontotemporal dementia with parkinsonism linked to chromosome 17, corticobasal degeneration, and Niemann-Pick disease type C as well as in amyotrophic lateral sclerosis/Parkinson-dementia complex permit clinical characterization of the disease phenotypes and are crucial to the development and validation of biological markers for differential diagnostics and disease monitoring, for example, by use of neuroimaging or proteomic approaches. The wide pathologic and clinical spectrum of the tauopathies with parkinsonism is reviewed in this article, and perspectives on future advances in the understanding of the pathogenesis are given, together with potential therapeutic strategies.

Delineation of early changes in cases with progressive supranuclear palsy-like pathology. Astrocytes in striatum are primary targets of tau phosphorylation and GFAP oxidation

Progressive supranuclear palsy (PSP) is a complex tauopathy usually confirmed at post-mortem in advanced stages of the disease. Early PSP-like changes that may outline the course of the disease are not known. Since PSP is not rarely associated with argyrophilic grain disease (AGD) of varible intensity, the present study was focused on AGD cases with associated PSP-like changes in an attempt to delineate early PSP-like pathology in this category of cases. Three were typical clinical and pathological PSP. Another case presented with cognitive impairment, abnormal behavior and two falls in the last three months. One case suffered from mild cognitive impairment, and two had no evidence of neurological abnormality. Neuropathological study revealed, in addition to AGD, increased intensity and extent of lesion in three groups of regions, striatum, pallidus/subthalamus and selected nuclei of the brain stem, correlating with neurological impairment. Biochemical studies disclosed oxidative damage in the striatum and amygdala. Together the present observations suggest (i) early PSP-like lesions in the striatum, followed by the globus pallidus/subthalamus and selected nuclei of the brain stem; (ii) early involvement of neurons and astrocytes, but late appearance of tufted astrocytes; and (iii) oxidative damage of glial acidic protein in the striatum.

Characterization of dopaminergic dysfunction in familial progressive supranuclear palsy: an 18F-dopa PET study

We analyzed (18)F-dopa PET data from 11 members of kindreds with familial progressive supranuclear palsy (PSP) to characterize their cerebral dopaminergic dysfunction. Three clinically-affected PSP patients showed reduced (18)F-dopa uptake in the striatum, orbitofrontal cortex and amygdala. One asymptomatic subject exhibited progressive putamen dopaminergic dysfunction. 60% of subjects with abnormal (18)F-dopa scans developed PSP subsequently. This is the first in vivo documentation of cortical dopaminergic deficiency in PSP. Reduced striatal (18)F-dopa uptake in susceptible relatives may predict later clinical disease.

Neuroimaging and therapeutics in movement disorders

In this review, we discuss the role of neuroimaging in assessing treatment options for movement disorders, particularly Parkinson's disease (PD). Imaging methods to assess dopaminergic function have recently been applied in trials of potential neuroprotective agents. Other imaging methods using regional metabolism and/or cerebral perfusion have been recently introduced to quantify the modulation of network activity as an objective marker of the treatment response. Both imaging strategies have provided novel insights into the mechanisms underlying a variety of pharmacological and stereotaxic surgical treatment strategies for PD and other movement disorders.

A comparison of degeneration in motor thalamus and cortex between progressive supranuclear palsy and Parkinson's disease

Changes in motor cortical activation are associated with the major symptoms observed in both Parkinson's disease and progressive supranuclear palsy (PSP). While research has concentrated on basal ganglia abnormalities as central to these cortical changes, several studies in both disorders have shown pathology in the thalamus and motor cortices. In particular, we recently reported an 88% loss of corticocortical projection neurones in the pre-supplementary motor (pre-SMA) cortex in Parkinson's disease. Further analysis of the degree of neuronal loss and pathology in motor cortices and their thalamocortical relays in Parkinson's disease and PSP is warranted. Six cases with PSP, nine cases with Parkinson's disease and nine controls were selected from a prospectively studied brain donor cohort. alpha-Synuclein, ubiquitin and tau immunohistochemistry were used to identify pathological lesions. Unbiased stereological methods were used to analyse atrophy and neuronal loss in the motor thalamus [ventral anterior, ventrolateral anterior and ventrolateral posterior (VLp) nuclei] and motor cortices (primary motor, dorsolateral premotor and pre-SMA cortices). Analysis of variance and post hoc testing was used to determine differences between groups. In Parkinson's disease, the motor thalamus and motor cortices (apart from the pre-SMA) were preserved containing only rare alpha-synuclein-positive and ubiquitin-positive Lewy bodies. In contrast, patients with PSP had significant atrophy and neuronal loss in VLp (22 and 30%, respectively), pre-SMA (21 and 51%, respectively) and primary motor cortices (33 and 54%, respectively). In the primary motor cortex of PSP cases, neuronal loss was confined to inhibitory interneurones, whereas in the pre-SMA both interneurones (reduced by 26%) and corticocortical projection neurones (reduced by 82%) were affected. Tau-positive neurofibrillary and glial tangles were observed throughout the motor thalamus and motor cortices in PSP. These non-dopaminergic lesions in motor circuits are likely to contribute to the pathogenesis of both PSP and Parkinson's disease. The selective involvement of the VLp and primary motor cortex in PSP implicates these cerebellothalamocortical pathways as differentiating this disease, possibly contributing to the early falls.

FDG PET in the differential diagnosis of parkinsonian disorders

The differential diagnosis of parkinsonian disorders can be challenging, especially early in the disease course. PET imaging with [(18)F]-fluorodeoxyglucose (FDG) has been used to identify characteristic patterns of regional glucose metabolism in patient cohorts with idiopathic Parkinson's disease (PD), as well as variant forms of parkinsonism such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBGD). In this study, we assessed the utility of FDG PET in the differential diagnosis of individual patients with clinical parkinsonism. 135 parkinsonian patients were referred for FDG PET to determine whether their diagnosis could be made accurately based upon their scans. Imaging-based diagnosis was obtained by visual assessment of the individual scans and also by computer-assisted interpretation. The results were compared with 2-year follow-up clinical assessments made by independent movement disorders specialists who were blinded to the original PET findings. We found that blinded computer assessment agreed with clinical diagnosis in 92.4% of all subjects (97.7% early PD, 91.6% late PD, 96% MSA, 85% PSP, 90.1% CBGD, 86.5% healthy control subjects). Concordance of visual inspection with clinical diagnosis was achieved in 85.4% of the patients scanned (88.4% early PD, 97.2% late PD, 76% MSA, 60% PSP, 90.9% CBGD, 90.9% healthy control subjects). This study demonstrates that FDG PET performed at the time of initial referral for parkinsonism accurately predicted the clinical diagnosis of individual patients made at subsequent follow-up. Computer-assisted methodologies may be particularly helpful in situations where experienced readers of FDG PET images are not readily available.

Role of [18F]-dopa-PET imaging in assessing movement disorders

FD-PET has proved to be an extremely useful technique for the noninvasive evaluation of nigrostriatal pathophysiology in patients with PD and other movement disorders. The development of ratio methods for image analysis has greatly reduced the complexity of these PET studies and has facilitated data analysis. With the recent advances in cyclotron targetry and automated synthesis modules FD-PET will soon become an important component of the clinical armamentarium.

Genetic linkage of autosomal dominant progressive supranuclear palsy to 1q31.1

Progressive supranuclear palsy (PSP) is a disorder of unknown pathogenesis. Familial clusters of PSP have been reported related to mutations of protein tau. We report the linkage of a large Spanish family with typical autosomal dominant PSP to a new locus in chromosome 1. Four members of this family had typical PSP, confirmed by neuropathology in one case. At least five ancestors had similar disease. Other members of the family have incomplete phenotypes. The power of the linkage analysis was increased by detecting presymptomatic individuals with 18F-fluoro-dopa and 18F-deoxyglucose positron emission tomography. We screened the human genome with 340 polymorphic markers and we enriched the areas of interest with additional markers. The disease status was defined according to the clinical and positron emission tomography data. We excluded linkage to the tau gene in chromosome 17. PSP was linked, in this family, to one area of 3.4 cM in chromosome 1q31.1, with a maximal multipoint < OD score of +3.53. This area contains at least three genes, whose relevance in PSP is unknown. We expect to further define the gene responsible for PSP, which could help to understand the pathogenesis of this disease and to design effective treatment.

Accuracy of clinical diagnosis of progressive supranuclear palsy

We assessed the accuracy of clinical diagnosis of progressive supranuclear palsy (PSP, Steele-Richardson-Olszewski disease) and the validity of existing sets of clinical diagnostic criteria for PSP (see Appendix) using neuropathologically examined cases from the Queen Square Brain Bank for Neurological Disorders. Diagnosis of PSP was made by 40 different physicians, and 60 cases clinically diagnosed as PSP when last assessed in life were studied. In 47 cases (78%), the diagnosis of PSP was confirmed pathologically. False-positive diagnoses included Parkinson's disease with significant additional cortical Lewy body (n = 3) or Alzheimer (n = 1) pathology, multiple system atrophy (n = 4), and corticobasal degeneration, Pick's disease, motor neurone disease, cerebrovascular disease, and a sporadic case of frontotemporal dementia and parkinsonism linked to chromosome 17 (1 case each). Most cases of PSP were diagnosed accurately by neurologists at the final assessment. Although application of National Institute of Neurological Disorders and the Society for PSP possible category marginally improved the accuracy of initial clinical diagnosis, none of the existing operational criteria could significantly improve accuracy of the final clinical diagnosis.

PET studies in dementia

Measurement of local cerebral glucose metabolism (lCMRGlc) by positron emission tomography (PET) and 18F-2-fluoro-2-deoxy-D-glucose (FDG) has become a standard technique during the past 20 years and is now available at many university hospitals in all highly developed countries. Many studies have documented a close relation between lCMRGlc and localized cognitive functions, such as language and visuoconstructive abilities. Alzheimer's disease (AD) is characterized by regional impairment of cerebral glucose metabolism in neocortical association areas (posterior cingulate, temporoparietal and frontal multimodal association cortex), whereas primary visual and sensorimotor cortex, basal ganglia, and cerebellum are relatively well preserved. In a multicenter study comprising 10 PET centers (Network for Efficiency and Standardisation of Dementia Diagnosis, NEST-DD) that employed an automated voxel-based analysis of FDG PET images, the distinction between controls and AD patients was 93% sensitive and 93% specific, and even in very mild dementia (at MMSE 24 or higher) sensitivity was still 84% at 93% specificity. Significantly abnormal metabolism in mild cognitive deficit (MCI) indicates a high risk to develop dementia within the next two years. Reduced neocortical glucose metabolism can probably be detected with FDG PET in AD on average one year before onset of subjective cognitive impairment. In addition to glucose metabolism, specific tracers for dopamine synthesis (18F-F-DOPA) and for (11C-MP4A) are of interest for differentiation among dementia subtypes. Cortical acetylcholine esterase activity (AChE) activity is significantly lower in patients with AD or with dementia with Lewy bodies (DLB) than in age-matched normal controls. In LBD there is also impairment of dopamine synthesis, similar to Parkinson disease.

Differentiating multiple system atrophy from Parkinson's disease: contribution of striatal and midbrain MRI volumetry and multi-tracer PET imaging

OBJECTIVES

The differential diagnosis between typical idiopathic Parkinson's disease (PD) and the striatonigral variant of multiple system atrophy (MSA-P) is often difficult because of the presence of signs and symptoms common to both forms of parkinsonism, particularly at symptom onset. This study investigated striatal and midbrain findings in MSA-P and PD patients in comparison with normal controls with the use of positron emission tomography (PET) and three dimensional magnetic resonance imaging (3D MRI) based volumetry to increase the differential diagnostic accuracy between both disease entities.

METHODS

Nine patients with MSA-P, 24 patients with PD, and seven healthy controls were studied by MRI and PET with 6-[(18)F]-fluoro-L-dopa (FDOPA), [(18)F]fluoro-deoxyglucose (FDG), and 11-C-Raclopride (RACLO). Striatal and extrastriatal volumes of interest (VOI) were calculated on the basis of the individual MRI data. The PET data were transferred to the VOI datasets and subsequently analysed.

RESULTS

MSA-P differed significantly from PD patients in terms of decreased putaminal volume, glucose metabolism, and postsynaptic D2 receptor density. The striatal FDOPA uptake was equally impaired in both conditions. Neither MRI volumetry nor PET imaging of the midbrain region further contributed to the differential diagnosis between PD and MSA-P.

CONCLUSIONS

The extent and spatial distribution of functional and morphological changes in the striatum permit the differentiation of MSA-P from PD. Both, multi-tracer PET and 3D MRI based volumetry, may be considered equivalent in the assessment of different striatal abnormality in both disease entities. In contrast, MRI and PET imaging of the midbrain does not provide a further gain in diagnostic accuracy.

Progressive supranuclear palsy: where are we now?

This review provides an update on progressive supranuclear palsy (PSP, or Steele-Richardson-Olszewski disease), an adult-onset neurodegenerative disorder characterised by early postural instability, which leads to falls, and a vertical supranuclear-gaze palsy. Recent epidemiological studies have shown that the disorder is more common than previously recognised, that it is commonly misdiagnosed, and that it may present to a wide range of hospital specialists. The diagnosis of PSP hinges on clinical acumen. Attempts to identify a suitable biomarker in the CSF or a specific and sensitive imaging or neurophysiological technique have so far failed to have a significant effect on the diagnostic process. Better understanding of the molecular pathology of PSP has highlighted the importance of tau-protein accumulation and tau-genotype susceptibility in its pathogenesis. No drug treatment significantly and consistently benefits patients, and novel therapies are urgently required.

Parkinsonian syndromes and differential diagnosis

PURPOSE OF REVIEW

Physicians are becoming more astute at diagnosing the various parkinsonian syndromes but in clinical practice it is still often difficult to make the correct diagnosis. This review discusses new evidence that may aid physicians in correctly identifying parkinsonian syndromes.

RECENT FINDINGS

We will review the newest developments in the areas of clinical features, electrophysiologic tests, autonomic tests, neuropsychologic tests, imaging, and biochemical markers which may be of value in differentiating these syndromes.

SUMMARY

Accurate diagnosis of the parkinsonian syndromes has important implications for patients, in terms of both prognosis and management. Investigations reported during the last year provide new insight into the distinguishing features of these syndromes and may help clinicians and researchers define these disorders more precisely.