Neurophysiologic evaluation and clinical trials for neuromuscular diseases

Thermal perception thresholds recorded using method of limits change over brief time intervals

Quantitative Sensory Testing (QST) of thermal perception thresholds assesses small afferent nerve function. QST has also been widely used to investigate the effects of interventions on the perception of activity within these nerve fibres, often over brief time periods. The natural variation in perception thresholds over brief time periods has not been determined, however, complicating accurate identification of induced changes. The present study therefore investigated changes in thermal perception threshold values within a 1-h period. Twenty-four healthy women volunteers aged 18-28 years (mean 20.6, SD 2.8) undertook cold sensation (CS), warm sensation (WS), cold pain (CP), and hot pain (HP) perception threshold measurements on the thenar eminence of the dominant hand during six 8-min experimental cycles. The order of stimulus presentation was randomized within pre-selected criteria. An adaptation temperature of 32 degrees C, a rate of temperature change of 0.5 degrees C/s, a 3 cm x 3 cm thermode, and a method of limits algorithm were used. Separate two-way ANOVAs with repeated measures showed statistically significant changes over time for WS, CS, and HP (p < 0.05), but not for CP (p = 0.232). The results indicate that WS, CS, and HP perception thresholds change significantly with repeated testing over a 1-h period. These results should be carefully considered when assessing the importance of observed changes in thermal perception thresholds. In research trials exclusion of a control group would be a fundamental flaw.

Endothelial and neural regulation of skin microvascular blood flow in patients with diabetic peripheral neuropathy: effect of treatment with the isoform-specific protein kinase C beta inhibitor, ruboxistaurin

PURPOSE

This article aims to study the effects of ruboxistaurin (RBX) on skin microvascular blood flow (SkBF) and evaluate the relationship between endothelial and neural control of SkBF in patients with diabetic peripheral neuropathy (DPN).

METHODS

We studied 11 placebo- and 9 RBX (32 mg/day)-treated patients who participated in a 1-year, double-masked, randomized, Phase 3 study of RBX for treatment of DPN sensory symptoms. Patients had type 1 or type 2 diabetes, a detectable sural sensory nerve action potential, and Neuropathy Total Symptom Score-6 (NTSS-6) >6 points. SkBF was measured by laser Doppler velocimetry, combined with iontophoresis of acetylcholine and sodium nitroprusside, at baseline, 3 months, and 1 year. Sensory symptoms and electrophysiology were also evaluated during the study. The relationship between endothelial and neural control of SkBF at baseline was assessed using linear regression.

RESULTS

No significant differences (RBX vs. placebo) were demonstrable for post-iontophoresis SkBF [fold increase from basal state (1 year): endothelium-dependent, 3.6 vs. 8.6; endothelium-independent, 3.7 vs. 2.0; C fiber-mediated, 1.7 vs. 2.0; P>.05] or sensory symptoms [NTSS-6 total score (1 year): 7.7 vs. 6.0 points; P=.4]. There were also no significant between-group differences in nerve conduction parameters, except for placebo peroneal nerve conduction velocity, which demonstrated a statistically significant improvement of unknown clinical importance (Z=2.1; P=.034). At baseline, C fiber-mediated vasodilatation correlated well with endothelium-dependent vasodilation (r=.7, P<.01) but not with endothelium-independent vasodilatation (r=-.1, P=.7).

CONCLUSIONS

RBX demonstrated no effect on SkBF or sensory symptoms after 1 year in this cohort. The correlation between C fiber-mediated and endothelium-dependent SkBF at baseline suggests that improving endothelial function could affect the microcirculation not only locally but also via the neurovascular arcade.

Assessment of precision and reproducibility of a new myograph

Background

The physiological characteristics of muscle activity and the assessment of muscle strength represent important diagnostic information. There are many devices that measure muscle force in humans, but some require voluntary contractions, which are difficult to assess in weak or unconscious patients who are unable to complete a full range of voluntary force assessment tasks. Other devices, which obtain standard muscle contractions by electric stimulations, do not have the technology required to induce and measure reproducible valid contractions at the optimum muscle length.

Methods

In our study we used a newly developed diagnostic device which measures accurately the reproducibility and time-changed-variability of the muscle force in an individual muscle. A total of 500 in-vivo measurements of supra-maximal isometric single twitch contractions were carried out on the musculus adductor pollicis of 5 test subjects over 10 sessions, with ten repetitions per session. The same protocol was performed on 405 test subjects with two repetitions each to determine a reference-interval on healthy subjects.

Results

Using our test setting, we found a high reproducibility of the muscle contractions of each test subject. The precision of the measurements performed with our device was 98.74%. Only two consecutive measurements are needed in order to assess a real, representative individual value of muscle force. The mean value of the force of contraction was 9.51 N and the 95% reference interval was 4.77–14.25 N.

Conclusion

The new myograph is a highly reliable measuring device with which the adductor pollicis can be investigated at the optimum length. It has the potential to become a reliable and valid tool for diagnostic in the clinical setting and for monitoring neuromuscular diseases.

A 6-month, randomized, double-masked, placebo-controlled study evaluating the effects of the protein kinase C-beta inhibitor ruboxistaurin on skin microvascular blood flow and other measures of diabetic peripheral neuropathy

OBJECTIVE

Diabetes leads to protein kinase C (PKC)-beta overactivation and microvascular dysfunction, possibly resulting in disordered skin microvascular blood flow (SkBF) and other changes observed in diabetic peripheral neuropathy (DPN) patients. We investigate the effects of the isoform-selective PKC-beta inhibitor ruboxistaurin mesylate on neurovascular function and other measures of DPN.

RESEARCH DESIGN AND METHODS

Endothelium-dependent and C fiber-mediated SkBF, sensory symptoms, neurological deficits, nerve fiber morphometry, quantitative sensory and autonomic function testing, nerve conduction studies, quality of life (using the Norfolk Quality-of-Life Questionnaire for Diabetic Neuropathy [QOL-DN]), and adverse events were evaluated for 20 placebo- and 20 ruboxistaurin-treated (32 mg/day) DPN patients (aged > or =18 years; with type 1 or type 2 diabetes and A1C < or =11%) during a randomized, double-masked, single-site, 6-month study.

RESULTS

Endothelium-dependent (+78.2%, P < 0.03) and C fiber-mediated (+56.4%, P < 0.03) SkBF at the distal calf increased from baseline to end point. Significant improvements from baseline within the ruboxistaurin group were also observed for the Neuropathy Total Symptom Score-6 (NTSS-6) (3 months -48.3%, P = 0.01; end point -66.0%, P < 0.0006) and the Norfolk QOL-DN symptom subscore and total score (end point -41.2%, P = 0.01, and -41.0, P = 0.04, respectively). Between-group differences in baseline-to-end point change were observed for NTSS-6 total score (placebo -13.1%; ruboxistaurin -66.0%, P < 0.03) and the Norfolk QOL-DN symptom subscore (placebo -4.0%; ruboxistaurin -41.2%, P = 0.041). No significant ruboxistaurin effects were demonstrated for the remaining efficacy measures. Adverse events were consistent with those observed in previous ruboxistaurin studies.

CONCLUSIONS

In this cohort of DPN patients, ruboxistaurin enhanced SkBF at the distal calf, reduced sensory symptoms (NTSS-6), improved measures of Norfolk QOL-DN, and was well tolerated.

Pulmonary complications of chronic neuromuscular diseases and their management

Chronic neuromuscular diseases may affect all major respiratory muscles groups including inspiratory, expiratory, and bulbar, and respiratory complications are the major cause of morbidity and mortality. Untreated, many of these diseases lead inexorably to hypercapnic respiratory failure, precipitated in some cases by chronic aspiration and secretion retention or pneumonia, related to impairment of cough and swallowing mechanisms. Many measures are helpful including inhibition of salivation, cough-assist techniques, devices to enhance communication, and physical therapy. In addition, ventilatory assistance is an important part of disease management for patients with advanced neuromuscular disease. Because of its comfort, convenience, and portability advantages, noninvasive positive pressure ventilation (NPPV) has become the modality of first choice for most patients. Patients to receive NPPV should be selected using consensus guidelines, and initiation should be gradual to maximize the chances for success. Attention should be paid to individual preferences for interfaces and early identification of cough impairment that necessitates the use of cough-assist devices. For patients considered unsuitable for noninvasive ventilation, invasive mechanical ventilation should be considered, but only after a frank but compassionate discussion between the patient, family, physician, and other caregivers.

Reproducibility of neurophysiological and myometric measurement in the ulnar nerve-abductor digiti minimi system

Reliability in strength and neurophysiological measurements is important in evaluating progression of neuromuscular diseases. No data are available on the variability of neurophysiological parameters as compared with maximal voluntary isometric contraction (MVIC) in the same muscles, in healthy subjects. A control population of 26 healthy subjects was studied twice on different days. We evaluated the reliability of neurophysiological parameters obtained from bilateral ulnar nerve stimulation, recording the response over the abductor digiti minimi (ADM) muscle, including distal motor latency, compound muscle potential amplitude and area, F-wave frequency and mean F-wave latency, and the derived neurophysiological index that we have described previously. MVIC force was measured in each session in both ADM muscles. The variances between the grouped data obtained in the two recording sessions were identical, indicating a low intrinsic variability with this experimental methodology. Comparison of the mean values obtained in the two sessions revealed no statistically significant differences. The reliability of these neurophysiological and strength measurements in the same nerve/muscle system suggests they may be useful in comparing the dynamics of weakness and neurophysiological change in neuromuscular disease.

Reliability of nerve conduction studies among active workers

Nerve conduction studies play an important role in clinical practice and research. Given their widespread use, reliability of tests merits careful attention. We assessed interexaminer and intraexaminer reliability of median and ulnar sensory nerve measures of amplitude, onset latency, and peak latency. In a two-phase cross-sectional study, two examiners tested 158 workers. Reliability was assessed with intraclass correlations (ICC) and kappa statistics. Median nerve measures were more reliable (ICC range, 0.76 to 0.92) than ulnar measures (ICC range, 0.22 to 0.85). Ulnar-onset latencies had the worst reliability. The median-ulnar peak latency difference was a particularly stable measure (ICC range, 0.79 to 0.92). The median-ulnar peak latency difference had high interexaminer reliability (kappa range, 0.71 to 0.79) for normal tests defined by cut points of 0.8 ms and 0.5 ms. Intraexaminer reliability was higher with the 0.8-ms cut point (kappa = 0.90 and kappa = 0.85 for examiners 1 and 2, respectively). Rather than absolute cut points to describe normality, a more rational interpretation of results can be made with ordered categories or continuous measures.