Reference values for nerve conduction studies of the peroneal, tibial, and sural nerve derived from a large population-based cohort: Associations with demographic and anthropometric characteristics-The Maastricht study

INTRODUCTION/AIMS

Nerve conduction studies (NCSs) are widely used to support the clinical diagnosis of neuromuscular disorders. The aims of this study were to obtain reference values for peroneal, tibial, and sural NCSs and to examine the associations with demographic and anthropometric factors.

METHODS

In 5099 participants (aged 40-79 years) without type 2 diabetes of The Maastricht Study, NCSs of peroneal, tibial, and sural nerves were performed. Values for compound muscle action potential (CMAP) and sensory nerve action potential amplitude, nerve conduction velocity (NCV), and distal latency were acquired. The association of age, sex, body mass index (BMI), and height with NCS values was determined using uni- and multivariate linear regression analyses.

RESULTS

Detailed reference values are reported per decade for men and women. Significantly lower NCVs and longer distal latencies were observed in all nerves in older and taller individuals as well as in men. In these groups, amplitudes of the tibial and sural nerves were significantly lower, whereas a lower peroneal nerve CMAP was only significantly associated with age. BMI showed a multidirectional association. After correction for anthropometric factors in the multivariate analysis, the association between sex and NCS values was less straightforward.

DISCUSSION

These values from a population-based dataset could be used as a reference for generating normative values. Our findings show the association of NCS values with anthropometric factors. In clinical practice, these factors can be considered when interpreting NCS values.

Cardiovagal baroreflex sensitivity, blood pressure and blood pressure variability - the Maastricht study

OBJECTIVE

Low baroreflex sensitivity (BRS) has been hypothesized to underlie high blood pressure (BP) and greater BP variability on the longer term, but evidence is scarce. In addition, these associations may differ by sex and (pre)diabetes. Therefore, we investigated whether cardiovagal BRS is associated with short- to mid-term mean BP and BP variability, and differs according to sex and (pre)diabetes.

METHODS

Cross-sectional data from the population-based Maastricht study (age 60 ± 8 years, 52% men), where office ( n  = 2846), 24-h ( n  = 2404) and 7-day BP measurements ( n  = 2006) were performed. Spontaneous BRS was assessed by cross-correlating systolic BP and instantaneous heart rate. We used linear regression with adjustments for age, sex, BP or BP variability, and cardiovascular risk factors.

RESULTS

With regard to BP, 1-SD (standard deviation) lower BRS (-5.75 ms/mmHg) was associated with higher office, 24-h and 7-day systolic BP (2.22 mmHg [95% confidence interval [CI]: 1.59; 2.80], 0.95 mmHg [0.54; 1.36], and 1.48 mmHg [0.99; 1.97], respectively) and diastolic BP (1.31 mmHg [0.97; 1.66], 0.57 mmHg [0.30; 0.84], and 0.86 mmHg [0.54; 1.17], respectively). Per 1-SD lower BRS, these associations were stronger in women (0.5-1.5 mmHg higher compared to men), and weaker in those with type 2 diabetes (1-1.5 mmHg lower compared to normal glucose metabolism). With regard to BP variability, BRS was not consistently associated with lower BP variability.

CONCLUSIONS

Lower cardiovagal BRS is associated with higher mean BP from the short- to mid-term range, and not consistently with BP variability. The associations with mean BP are stronger in women and weaker in those with type 2 diabetes.

Sex differences in the association of prediabetes and type 2 diabetes with microvascular complications and function: The Maastricht Study

BACKGROUND

Women with type 2 diabetes are disproportionally affected by macrovascular complications; we here investigated whether this is also the case for microvascular complications and retinal microvascular measures.

METHODS

In a population-based cohort study of individuals aged 40-75 years (n = 3410; 49% women, 29% type 2 diabetes (oversampled by design)), we estimated sex-specific associations, and differences therein, of (pre)diabetes (reference: normal glucose metabolism), and of continuous measures of glycemia with microvascular complications and retinal measures (nephropathy, sensory neuropathy, and retinal arteriolar and venular diameters and dilatation). Sex differences were analyzed using regression models with interaction terms (i.e. sex-by- (pre)diabetes and sex-by-glycemia) and were adjusted for potential confounders.

RESULTS

Men with type 2 diabetes (but not those with prediabetes) compared to men with normal glucose metabolism, (and men with higher levels of glycemia), had significantly higher prevalences of nephropathy (odds ratio: 1.58 95% CI (1.01;2.46)) and sensory neuropathy (odds ratio: 2.46 (1.67;3.63)), larger retinal arteriolar diameters (difference: 4.29 µm (1.22;7.36)) and less retinal arteriolar dilatation (difference: - 0.74% (- 1.22; - 0.25)). In women, these associations were numerically in the same direction, but generally not statistically significant (odds ratios: 1.71 (0.90;3.25) and 1.22 (0.75;1.98); differences: 0.29 µm (- 3.50;4.07) and: - 0.52% (- 1.11;0.08), respectively). Interaction analyses revealed no consistent pattern of sex differences in the associations of either prediabetes or type 2 diabetes or glycemia with microvascular complications or retinal measures. The prevalence of advanced-stage complications was too low for evaluation.

CONCLUSIONS

Our findings show that women with type 2 diabetes are not disproportionately affected by early microvascular complications.

Associations of cells from both innate and adaptive immunity with lower nerve conduction velocity: the Maastricht Study

INTRODUCTION

Distal sensorimotor polyneuropathy (DSPN) is common in people with diabetes but is also found in pre-diabetes. Peripheral nerve myelin damage, which can be assessed by reduced nerve conduction velocity (NCV), is an essential feature of DSPN. Emerging evidence indicates that the development of DSPN may involve the activation of the immune system. However, available studies have mainly investigated circulating immune mediators, whereas the role of immune cells remains unclear. Therefore, we aimed to test whether leukocyte subsets are associated with NCV.

RESEARCH DESIGN AND METHODS

This cross-sectional study analyzed data from 850 individuals (of whom 252 and 118 had type 2 diabetes and pre-diabetes, respectively) of the Maastricht Study. NCV was measured in the peroneal and tibial motor nerves and the sural sensory nerve and summed to calculate a standardized NCV sum score. Associations between percentages of leukocyte subsets and NCV sum scores were estimated using linear regression models adjusted for demographic, lifestyle, metabolic and clinical covariates.

RESULTS

After adjustment for covariates, higher percentages of basophils and CD4⁺ T cells were associated with lower NCV (p=0.014 and p=0.005, respectively). The percentage of CD8⁺ T cells was positively associated with NCV (p=0.022). These associations were not modified by glucose metabolism status (all p_interaction >0.05). No associations were found for monocytes, eosinophils, neutrophils, lymphocytes, total T cells, Treg cells and B cells.

CONCLUSIONS

The associations of basophils, CD4⁺ and CD8⁺ T cells with NCV suggest that cell types from both innate and adaptive immunity may be implicated in the development of DSPN.

Cardiometabolic risk factors as determinants of peripheral nerve function: the Maastricht Study

AIMS/HYPOTHESIS

We aimed to examine associations of cardiometabolic risk factors, and (pre)diabetes, with (sensorimotor) peripheral nerve function.

METHODS

In 2401 adults (aged 40-75 years) we previously determined fasting glucose, HbA_1c, triacylglycerol, HDL- and LDL-cholesterol, inflammation, waist circumference, blood pressure, smoking, glucose metabolism status (by OGTT) and medication use. Using nerve conduction tests, we measured compound muscle action potential, sensory nerve action potential amplitudes and nerve conduction velocities (NCVs) of the peroneal, tibial and sural nerves. In addition, we measured vibration perception threshold (VPT) of the hallux and assessed neuropathic pain using the DN4 interview. We assessed cross-sectional associations of risk factors with nerve function (using linear regression) and neuropathic pain (using logistic regression). Associations were adjusted for potential confounders and for each other risk factor. Associations from linear regression were presented as standardised regression coefficients (β) and 95% CIs in order to compare the magnitudes of observed associations between all risk factors and outcomes.

RESULTS

Hyperglycaemia (fasting glucose or HbA_1c) was associated with worse sensorimotor nerve function for all six outcome measures, with associations of strongest magnitude for motor peroneal and tibial NCV, β_{fasting glucose} = -0.17 SD (-0.21, -0.13) and β_{fasting glucose} = -0.18 SD (-0.23, -0.14), respectively. Hyperglycaemia was also associated with higher VPT and neuropathic pain. Larger waist circumference was associated with worse sural nerve function and higher VPT. Triacylglycerol, HDL- and LDL-cholesterol, and blood pressure were not associated with worse nerve function; however, antihypertensive medication usage (suggestive of history of exposure to hypertension) was associated with worse peroneal compound muscle action potential amplitude and NCV. Smoking was associated with worse nerve function, higher VPT and higher risk for neuropathic pain. Inflammation was associated with worse nerve function and higher VPT, but only in those with type 2 diabetes. Type 2 diabetes and, to a lesser extent, prediabetes (impaired fasting glucose and/or impaired glucose tolerance) were associated with worse nerve function, higher VPT and neuropathic pain (p for trend <0.01 for all outcomes).

CONCLUSIONS/INTERPRETATION

Hyperglycaemia (including the non-diabetic range) was most consistently associated with early-stage nerve damage. Nonetheless, larger waist circumference, inflammation, history of hypertension and smoking may also independently contribute to worse nerve function.

Improved epileptic seizure detection combining dynamic feature normalization with EEG novelty detection

Continuous electroencephalographic monitoring of critically ill patients is an established procedure in intensive care units. Seizure detection algorithms, such as support vector machines (SVM), play a prominent role in this procedure. To correct for inter-human differences in EEG characteristics, as well as for intra-human EEG variability over time, dynamic EEG feature normalization is essential. Recently, the median decaying memory (MDM) approach was determined to be the best method of normalization. MDM uses a sliding baseline buffer of EEG epochs to calculate feature normalization constants. However, while this method does include non-seizure EEG epochs, it also includes EEG activity that can have a detrimental effect on the normalization and subsequent seizure detection performance. In this study, EEG data that is to be incorporated into the baseline buffer are automatically selected based on a novelty detection algorithm (Novelty-MDM). Performance of an SVM-based seizure detection framework is evaluated in 17 long-term ICU registrations using the area under the sensitivity-specificity ROC curve. This evaluation compares three different EEG normalization methods, namely a fixed baseline buffer (FB), the median decaying memory (MDM) approach, and our novelty median decaying memory (Novelty-MDM) method. It is demonstrated that MDM did not improve overall performance compared to FB (p < 0.27), partly because seizure like episodes were included in the baseline. More importantly, Novelty-MDM significantly outperforms both FB (p = 0.015) and MDM (p = 0.0065).

Optimal training dataset composition for SVM-based, age-independent, automated epileptic seizure detection

Automated seizure detection is a valuable asset to health professionals, which makes adequate treatment possible in order to minimize brain damage. Most research focuses on two separate aspects of automated seizure detection: EEG feature computation and classification methods. Little research has been published regarding optimal training dataset composition for patient-independent seizure detection. This paper evaluates the performance of classifiers trained on different datasets in order to determine the optimal dataset for use in classifier training for automated, age-independent, seizure detection. Three datasets are used to train a support vector machine (SVM) classifier: (1) EEG from neonatal patients, (2) EEG from adult patients and (3) EEG from both neonates and adults. To correct for baseline EEG feature differences among patients feature, normalization is essential. Usually dedicated detection systems are developed for either neonatal or adult patients. Normalization might allow for the development of a single seizure detection system for patients irrespective of their age. Two classifier versions are trained on all three datasets: one with feature normalization and one without. This gives us six different classifiers to evaluate using both the neonatal and adults test sets. As a performance measure, the area under the receiver operating characteristics curve (AUC) is used. With application of FBC, it resulted in performance values of 0.90 and 0.93 for neonatal and adult seizure detection, respectively. For neonatal seizure detection, the classifier trained on EEG from adult patients performed significantly worse compared to both the classifier trained on EEG data from neonatal patients and the classier trained on both neonatal and adult EEG data. For adult seizure detection, optimal performance was achieved by either the classifier trained on adult EEG data or the classifier trained on both neonatal and adult EEG data. Our results show that age-independent seizure detection is possible by training one classifier on EEG data from both neonatal and adult patients. Furthermore, our results indicate that for accurate age-independent seizure detection, it is important that EEG data from each age category are used for classifier training. This is particularly important for neonatal seizure detection. Our results underline the under-appreciated importance of training dataset composition with respect to accurate age-independent seizure detection.

Optimizing temperature threshold testing in small-fiber neuropathy

INTRODUCTION

We examined optimization of a temperature threshold testing (TTT) protocol for patients with suspected small-fiber neuropathy (SFN) to lessen the burden for both patients and technicians, without sacrificing accuracy.

METHODS

Data from 81 patients with SFN (skin biopsy and TTT abnormal) and 81 without SFN (skin biopsy and TTT normal) were used. Warm, cold, and heat pain sensation thresholds were determined bilaterally on the thenar eminence and foot dorsum by methods of limits and levels. Diagnostic accuracy was determined for various sensory modality combinations through comparative corresponding area under the receiver-operator characteristic curves.

RESULTS

Assessment of warm and cold thresholds in all extremities by the method of levels showed the best discriminatory ability (area under the curve 0.95, sensitivity 84.2%, specificity 93.8%).

CONCLUSIONS

These assessments are suggested for TTT examination in possible SFN patients. By applying this combination, the time needed for TTT can be reduced, maintaining diagnostic accuracy.

Assessment of dynamic cerebral autoregulation and cerebral carbon dioxide reactivity during normothermic cardiopulmonary bypass

Despite increased risk of neurological complications after cardiac surgery, monitoring of cerebral hemodynamics during cardiopulmonary bypass (CPB) is still not a common practice. Therefore, a technique to evaluate dynamic cerebral autoregulation and cerebral carbon dioxide reactivity (CO2R) during normothermic nonpulsatile CPB is presented. The technique uses continuous recording of invasive arterial blood pressure, middle cerebral artery blood flow velocity, absolute cerebral tissue oxygenation, in-line arterial carbon dioxide levels, and pump flow measurement in 37 adult male patients undergoing elective CPB. Cerebral autoregulation is estimated by transfer function analysis and the autoregulation index, based on the response to blood pressure variation induced by cyclic 6/min changes of indexed pump flow from 2.0 to 2.4 up to 2.8 L/min/m(2). CO2R was calculated from recordings of both cerebral blood flow velocity and cerebral tissue oxygenation. Cerebral autoregulation and CO2R were estimated at hypocapnia, normocapnia, and hypercapnia. CO2R was preserved during CPB, but significantly lower for hypocapnia compared with hypercapnia (p < 0.01). Conversely, cerebral autoregulation parameters such as gain, phase, and autoregulation index were significantly higher (p < 0.01) during hypocapnia compared with both normocapnia and hypercapnia. Assessing cerebral autoregulation and CO2R during CPB, by cyclic alteration of pump flow, showed an impaired cerebral autoregulation during hypercapnia.

Increased contact heat evoked potential stimulation latencies in responders to spinal cord stimulation for painful diabetic polyneuropathy

OBJECTIVES

To analyze sensory characteristics and small nerve fiber function in patients suffering from painful diabetic polyneuropathy (PDP) and compare outcomes in responders and nonresponders to SCS treatment.

METHODS

Fifteen patients with intractable PDP in the legs were recruited. If trial stimulation resulted in clinically relevant pain relief, a pulse generator was implanted and pain scores were measured after 12 months. Sensory characteristics (modified Inflammatory Neuropathy Cause and Treatment [md-INCAT] sum score) and small nerve fiber function (contact heat evoked potentials, CHEPs) were measured before implantation (D1), and CHEP measurement was repeated after two weeks of trial stimulation (D2). Outcomes in responders (N = 10) and nonresponders (N = 5) to SCS treatment were compared. Data were analyzed using nonparametric statistics.

RESULTS

At one year, clinically relevant pain relief was achieved in 10 out of 15 patients. The md-INCAT score did not differ between SCS responders and nonresponders (8.0 vs. 5.0; p = 0.59). No differences were found in CHEP outcomes at D1 vs. D2, except for dorsal forearm P2 latency, and the correlation between D1 and D2 CHEP outcomes was high. Volar N2 forearm latency (0.492 vs. 0.434; p < 0.01), dorsal forearm N2 latency (0.518 vs. 0.453; p = 0.04), and dorsal forearm P2 latency (0.660 vs. 0.589; p = 0.04) were increased in SCS responders as compared with SCS nonresponders.

CONCLUSIONS

From this small-scale clinical pilot study we conclude that forearm CHEP latencies are increased in PDP patients who respond to SCS therapy as compared with SCS nonresponders. Before the CHEP latency can be used as a predictor of SCS outcome in PDP patients, a large-scale study is needed.

Temperature threshold testing: a systematic review

The diagnosis of small fiber neuropathy (SFN) has been recently defined as typical symptoms due to small nerve fiber dysfunction accompanied by reduced intra-epidermal nerve fiber density (IENFD) or abnormal temperature threshold testing (TTT). Guidelines have been published for the assessment of IENFD. However, international guidelines for TTT are lacking. This paper presents a systematic literature review on reported TTT methods and provides recommendations for its future use in studies evaluating patients. A total of 164 papers fulfilled pre-defined requirements and were selected for review. Over 15 types of instruments are currently being used with a variety of methodological approaches for location, stimulus application, and sensation qualities examined. Consensus is needed to standardize the use of TTT as a diagnostic and follow-up tool in patients.

Dynamic cerebral autoregulation: different signal processing methods without influence on results and reproducibility

Cerebral autoregulation controls cerebral blood flow under changing cerebral perfusion pressure. Standards for measurement and analysis of dynamic cerebral autoregulation (dCA) are lacking. In this study, dCA reproducibility, quantified by intraclass correlation coefficient, is evaluated for different methodological approaches of transfer function analysis (TFA) and compared with multimodal pressure flow analysis (MMPF). dCA parameters were determined in 19 healthy volunteers during three 15-min lasting epochs of spontaneous breathing. Every spontaneous breathing epoch was followed by 5 min of paced breathing at 6 cycles/min. These six measurements were performed in both a morning and an afternoon session. Analysis compared raw data pre-processing by mean subtraction versus smoothness priors detrending. The estimation of spectral density was either performed by averaging of subsequent time windows or by smoothing the spectrum of the whole recording. No significant influence of pre-processing and spectral estimation on dCA parameters was found. Therefore, there seems to be no need to prescribe a specific signal-processing regime. Poor reproducibility of gain and phase was found for TFA as well as for MMPF. Based on reproducibility, no preference can be made for morning versus afternoon measurements, neither for spontaneous versus paced breathing. Finally, reproducibility results are not in favour of TFA or MMPF.

The visually-evoked cerebral blood flow response in women with a recent history of preeclampsia and/or eclampsia

Several studies provide evidence for altered cerebral hemodynamics during (pre)eclampsia. Whether (pre)eclampsia has a persistent negative impact on cerebral hemodynamics, possibly contributing to an elevated risk of premature stroke, is unknown. The aims of this study were (i) to refine and apply a control system-based method previously introduced by Rosengarten to quantify the visually-evoked blood flow response of the posterior cerebral artery (PCA); and (ii) to test the hypothesis with this method that cerebral hemodynamics in women with a recent history of (pre)eclampsia is abnormal relative to that in parous controls. Hereto, we recorded cerebral blood flow velocity (CBFV) in the PCA by transcranial Doppler (TCD) sonography during cyclic visual stimulation in 15 former preeclamptics, 13 former eclamptics and 13 controls. The typical CBFV response was fitted with the step response of a second-order-linear model enabling quantification by parameters K (gain), zeta (damping), omega (natural frequency), T(v) (rate time) and T(d) (time delay). The method refinement introduced here consisted of response filtering before quantification and of considering the individual instead of group-averaged response patterns. Application of this refinement reduced the fitting errors (1.4 +/- 1.2 vs. 3.2 +/- 1.8, p < 0.01). Intergroup differences in model parameters were not found. Although statistically not significant, a trend was observed that critical damping (zeta>1) occurred more frequently in the combined group of former patients than in the controls (7 of 28 vs.1 of 13, p = 0.16). Critical damping (zeta>1) reflects an abnormal response, which is either compensated for by a rise in rate time ("intermediate"; zeta>1; T(v) > 20) or remains uncompensated ("sluggish"; zeta>1; T(v) < 20). Critical damping increased significantly (p = 0.039) with (pre-)eclampsia-to-test-interval in the PE+E patients with abnormal responses (zeta>1), suggesting that (pre)eclampsia might induce diminishing cerebral hemodynamic function over time. Based on a system-analytical classification approach, the data of this study provide evidence for individual CBFV responses to be abnormal in former (pre)eclamptics compared with controls. Further study is needed to reveal how the abnormal CBFV response classification reflects cerebrovascular dysfunction.

Improvement of small fiber neuropathy in a sarcoidosis patient after treatment with infliximab

We describe a patient with severe small fiber neuropathy (SFN) accompanied by autonomic involvement, who was experimentally treated with infliximab, an anti-tumour necrosis factor-alpha (TNF-alpha) therapy. Six months after this treatment was started his symptoms completely resolved. Until now they did not return. Repeated temperature threshold testing (TTT) as well as cardiovascular autonomic function test clearly improved after one year therapy. This case reveals two important issues. First, it shows that SFN seems not an irreversible disorder, even in severe cases. Second, TNF-alpha may be a crucial cytokine in the pathogenesis of SFN in sarcoidosis and eventually also in other immune mediated inflammatory diseases.

Association of small fiber neuropathy with cardiac sympathetic dysfunction in sarcoidosis

BACKGROUND AND AIM

Recently we found that small fiber neuropathy (SFN) occurs frequently in sarcoidosis. Autonomic dysfunction may be a feature of SFN. Since cardiac autonomic dysfunction has been identified as a strong predictor of morbidity and mortality, recognition of cardiac autonomic involvement is of clinical relevance. It was hypothesised that SFN might be related to cardiac sympathetic denervation in sarcoidosis.

METHODS

In the present study 45 consecutive sarcoidosis patients (13 without SFN assessed by thermal threshold testing (TTT), 32 with SFN (abnormal TTT) were enrolled. To rule out bias due to myocardial ischemia, cases with abnormal Thallium (201Tl) perfusion scintigraphy were excluded (n = 2). Cardiovascular autonomic function testing (Ewing tests) and 123I-MIBG (metaiodobenzylguanidine) scintigraphy were used to assess cardiac autonomic function. Further cardiac diagnostic work-up included ECG, Holter recording and echo Doppler cardiography.

RESULTS

Mild to moderate heterogeneity of 123I-MIBG uptake regional in the myocardium was demonstrated in a substantial number of the studied sarcoidosis population, especially in those with SFN (abnormal TTT). Mean inferior-anterior ratios were 0.85+/-0.17 (SFN) and 1.0+/-0.17 (no SFN; p = 0.003), respectively. Four out of the 14 cases with abnormal MIBG scintigraphy and SFN showed an abnormal Ewing test.

CONCLUSION

Cardiac sympathetic dysfunction assessed by use of 123I-MIBG myocardial scanning appeared to be heterogeneous in sarcoidosis patients and dependent on the presence or absence of SFN. MIBG scintigraphy may be of additional value in the management and follow-up of sarcoidosis patients. Future study is warranted to explore possible prognostic and therapeutic implications of these findings in sarcoidosis.

Small fiber neuropathy: a common and important clinical disorder

Small fiber neuropathy (SFN) is a neuropathy selectively involving small diameter myelinated and unmyelinated nerve fibers. Interest in this disorder has considerably increased during the past few years. It is often idiopathic and typically presents with peripheral pain and/or symptoms of autonomic dysfunction. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies (NCS) and abnormal specialized tests of small nerve fibers. Among others, these tests include assessment of epidermal nerve fiber density, temperature sensation tests for sensory fibers and sudomotor and cardiovagal testing (QSART) for autonomic fibers. Unless an underlying disease is identified, treatment is usually symptomatic and directed towards alleviation of neuropathic pain.

Abnormal warm and cold sensation thresholds suggestive of small-fibre neuropathy in sarcoidosis

OBJECTIVE

A substantial number of sarcoidosis patients report apparently non-specific symptoms such as pain, for which no organic substrate has yet been found. Recently we observed symptoms suggestive of small-fibre neuropathy in a group of sarcoidosis patients. The aim of the present study was to verify this observation using various electrophysiological tests.

METHODS

In 74 sarcoidosis patients complaining of symptoms suggestive of small-fibre neuropathy, thresholds for warm (WS) and cold sensation (CS) as well as for heat pain were determined at the thenar eminence and the foot dorsum. Furthermore, sympathetic skin responses (SSR), nerve conduction studies and concentric needle electromyography were performed. In 31 patients, cardiovascular autonomic testing was carried out.

RESULTS

Thermal threshold testing (TTT) revealed abnormalities in 51 of the 74 patients. Abnormalities showed an asymmetrical distribution. WS was affected more often than CS and feet more often than hands. Nerve conduction studies in the legs showed slightly abnormal results in 6 patients; all of these had abnormal TTT results. The SSR was absent at the foot in 7 patients. Cardiovascular autonomic testing was abnormal in only a single patient.

CONCLUSIONS

In a subgroup of sarcoidosis patients we found TTT abnormalities suggestive of small-fibre neuropathy. SSR and cardiovascular autonomic testing appeared to be of little diagnostic value. Small-fibre neuropathy may be the cause of a number of hitherto unexplained symptoms in sarcoidosis.

Neonatal electrocortical brain activity and cerebral tissue oxygenation during non-acidotic, normocarbic and normotensive graded hypoxemia

OBJECTIVE

Neonates are commonly exposed to isolated hypoxemic episodes. In order to identify the risk of this, we correlated cerebral oxygen delivery and electrocortical brain activity during isolated graded and repetitive hypoxemia in 1-week-old piglets.

METHODS

Six halothane-anesthetized piglets were subjected to two episodes of graded hypoxemia of 45 min duration. The fractional concentration of inspired oxygen (FiO(2)) was stepwise decreased at 15 min intervals from 0.21 to 0.15, 0.10 and 0.05. A second identical hypoxemic event was induced after 1 h of normoxemia (FiO(2) 0.21). Mean arterial pressure (MAP) and pH were maintained at baseline values during the whole experiment. We measured near infrared spectroscopy parameters (cerebral oxidized cytochrome aa(3) (Cytaa3), total hemoglobin (tHb: oxy- +deoxyhemoglobin)) corresponding to cerebral blood volume (CBV), carotid blood flow (Q(car)), intra-arterial oxygen saturation (SaO(2)), and mean maximal EEG amplitude and relative spectral power.

RESULTS

Delta (delta) power increased significantly and the EEG amplitude dropped below 10 and 5 microV at the end of the first and the second hypoxemic period (PaO(2) 2.68+/-1.08 (P<0.05) and 2.87+/-0.58 kPa, respectively). Both EEG variables normalized during recovery (FiO(2) 0.21). Q(car), CBV and Cytaa3 were not changed.

CONCLUSION

Acute isolated hypoxemia has to be sustained to induce neuronal hypofunction in normotensive animals. Hypoxic hypoxemia led to acute changes in neuronal activity, whereas cellular oxygenation remained unaffected.

Comparison of thermal threshold tests to assess small nerve fiber function: limits vs. levels

OBJECTIVE

The method of limits (MLI) and the method of levels (MLE) are psychophysical stimulus procedures most commonly applied to quantify warm and cold sensation thresholds in humans. This paper evaluates basic methodological properties of both methods and investigates the correspondence between the method's results.

METHODS

Warm sensation threshold was measured in 20 healthy participants using the psychophysical MLIs and MLEs. Two differently shaped kind of levels stimuli were used with triangular (TRIANG) and trapezoid (TRAP) temperature-time profile.

RESULTS

A linear model of temperature response, based on threshold level-crossing, quantifies sensation threshold, independent of the MLI inherent 'reaction-time' artifact. It results from modeling MLI responses to warm stimuli with different rates of temperature change. The model also quantifies the reaction-time delay in the physiological system from thermal stimulus presentation until manual response. This study shows that using the reaction-time independent MLE, TRAP should preferably be used for optimal quantification of sensation threshold.

CONCLUSIONS

Statistical testing shows that model-based MLI threshold equals MLE threshold provided MLE TRAP stimuli are used. Recommendations for optimal MLI and MLE stimulus configurations and properties are given in relation to application of quantitative sensory testing.

Small fibre neuropathy in sarcoidosis

Some patients with sarcoidosis have unexplained pain and dysaesthesia. We did quantitative sensory testing in 31 sarcoidosis patients with pain or autonomic dysfunction. 25 patients had reduced warmth sensitivity, cold sensitivity, or both. Intraepidermal nerve fibre density (IENFD) was measured in punch biopsy skin samples in seven consecutive patients. All seven patients had reduced IENFD compared with controls, which confirmed the presence of small fibre neuropathy in these patients. Some patients with sarcoidosis may have small fibre neuropathy with autonomic involvement.

Expectations of analgesia do not affect spinal nociceptive R-III reflex activity: an experimental study into the mechanism of placebo-induced analgesia

The purpose of this study was to investigate whether placebo analgesia is mediated by the release of beta-endorphin. In addition to subjective pain reports, we included an objective physiological parameter of nociception reflected by the opioid sensitive nociceptive R-III reflex. Placebo consisted of strong suggestions of pain relief and an intravenous injection of saline. Forty minutes after placebo, either the opioid antagonist naloxone or saline was administered intravenously without subjects noticing (hidden). Sixty healthy males, aged 18-30 years, voluntarily participated in this study. Subjects were randomized into one of four groups: group 1 received placebo and hidden naloxone, group 2 received hidden naloxone only, group 3 received placebo and hidden saline and group 4 received hidden saline only. Pain was induced by electrical stimulation of the sural nerve and evaluated with a visual analogue scale (VAS). In addition, changes in the magnitude of the nociceptive R-III reflex activity were assessed. We determined to what extent R-III reflex activity and subjective pain reports were decreased by placebo and we investigated whether these placebo-induced changes in reflex activity and subjective pain reports were naloxone reversible. Furthermore, we measured the degree of association between pain relief as measured on VAS and changes in R-III reflex activity. Finally, the role of beta-endorphin was assessed by measuring plasma endorphin levels before and after the administration of placebo. This study could not demonstrate a placebo effect as measured on VAS and R-III responses. The administration of placebo did not appear to have an effect on the release of beta-endorphins. Consistently, the antagonizing effects of naloxone were negligible. A subgroup analysis of those who did show a placebo response as indicated on the VAS did not support the supposition that beta-endorphin is released due to placebo suggestion. It is suggested that intensified stimuli and a more effective procedure to induce placebo analgesia (e.g. conditioning) may produce a proper placebo effect.