Motor root conduction block in the Lewis-Sumner syndrome.

BACKGROUND: The Lewis-Sumner syndrome (LSS) is a rare immune-mediated peripheral nerve disorder presenting with asymmetric upper limb sensory complaints and motor weakness. Asian patients with LSS have not been reported in the English literature. METHODS: Three Asian patients with features of LSS were prospectively studied. RESULTS: Our patients tended to older, female, and have involvement of the upper limbs exclusively than those in the West. They have a markedly longer disease duration before a diagnosis was made, which could also be the result of difficulty in eliciting motor root conduction block as a sign of proximal demyelination as observed in every patient. Pain is a universal feature as is sensory nerve conduction abnormality. None responded to immunotherapy, but disease stabilization was observed over the chronic course. CONCLUSIONS: Although rare, these unique observations in Asian patients with LSS differ from those reported in Western literature. The presence of motor root conduction block demonstrated for the first time is instrumental in establishing a diagnosis.

The laterality index in the evaluation of distal sensorimotor neuropathy.

OBJECTIVE: Electrodiagnostic evaluation of distal sensorimotor neuropathy can be technically challenging. Conventional nerve conduction studies (NCS) often include unilateral upper and lower limb evaluation for patients with suspected sensorimotor peripheral neuropathy. For patients with predominantly lower extremity complaints, NCS of both lower limbs are performed occasionally. Side-to-side NCS parameters have not been adequately addressed. METHODS: We performed NCS prospectively on 132 patients presenting with complaints of bilateral numbness or weakness in the extremities and 45 normal controls. The laterality index (LI) was defined as ratio of the smaller to the larger amplitude in a sensory or motor NCS, as a novel side-to-side comparison parameter. RESULTS: Ten patients had at least 1 sensory or motor NCS with LIs exceeding that of normal controls. Patients 1-7 (group 1) had diagnoses of autoimmune or neoplasia-related conditions and all had 3 or more NCS with abnormal LIs. In contrast, patients 8-10 (group 2) had diabetes mellitus and all had 2 or less NCS with abnormal LIs (unpaired t test; P = 0.002). In group 1, patients 1-4, 6, and 7 all had both upper and lower limb LI abnormalities. In contrast, only 1 patient (patient 9) had upper limb LI abnormality in group 2. CONCLUSIONS: Patients with abnormal LIs were uncommon in our cohort. Patients with diabetes mellitus had significantly less abnormal LIs than those with autoimmune or neoplasia-related etiologies. There is evidence of vasculitic inflammation documented in diabetic neuropathy. However, this process may be significantly less prominent compared with the former 2 conditions. Our findings of predominantly lower limb LI abnormalities suggest the presence of a length-dependent distal neuropathic process in diabetes mellitus. The LI is a simple and useful adjunct to detect asymmetrical NCS abnormalities. It may also provide helpful information regarding the underlying etiology.

Sensitivities of sensory nerve conduction study parameters in carpal tunnel syndrome.

It is generally accepted that median sensory nerve conduction studies are more sensitive than motor nerve conduction studies in the electrodiagnostic evidence of carpal tunnel syndrome (CTS). This study was conducted to compare the sensitivities of various parameters of sensory nerve conduction studies in the diagnosis of CTS. This prospective study included 88 consecutive patients (151 hands) with CTS and 106 control subjects. CTS was diagnosed clinically by two neurologists. Median sensory nerve responses with wrist stimulation were determined. The onset and peak latencies, peak-to-peak amplitudes, negative peak duration, and area were measured. The differences between the peak and onset latencies were also calculated as a measure of waveform temporal dispersion. Among each measured parameter, values between the 2.5th and the 97.5th percentile range of the control subjects served as the normal limits. Among the 151 hands with suspected CTS, five (3.3%) had normal electrodiagnostic studies and 146 (96.7%) had at least one abnormal electrodiagnostic study. Among the 146 hands with an abnormality, 138 had abnormal onset latency, 143 had abnormal peak latency, and 88 had abnormal difference between peak and onset latency. In addition, 87 had abnormal amplitude, 70 had abnormal duration, and 59 had abnormal area. The sensitivity was 91.4% for onset latency, 94.7% for peak latency, 58.3% for difference between peak and onset latency, 57.6% for amplitude, 46.4% for duration, and 39.1% for area. Our study shows that in patients with CTS, the most sensitive sensory nerve conduction parameter is the peak latency. Studying various additional sensory nerve conduction parameters did not significantly increase the diagnostic yield.

Pectoral nerve conduction studies: technique in healthy subjects and evaluation of brachial plexopathy.

OBJECTIVE: To define the optimal nerve conduction study (NCS) technique of the pectoral nerves and evaluate its clinical utility. DESIGN: Prospective electrophysiologic study with healthy controls. SETTING: Electrophysiologic laboratory in a large general hospital. PARTICIPANTS: Thirty healthy controls and 10 patients with cervical root or brachial plexus pathologies. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Correlation of pectoral NCS with electromyography and magnetic resonance imaging. RESULTS: For pectoral NCS, the mean values +/- standard deviation of onset latency, amplitude, and interside amplitude ratio (ratio of smaller over larger amplitude) were 2.01+/-0.22 ms, 11.75+/-2.21 mV, and .95+/-.04 mV, respectively. Subject age correlated significantly with both onset latency (r=.46, P<.001) and amplitude (r=-.34, P<.008). All 5 patients with brachial plexopathy had amplitude ratios below the normal limit of controls (.87). However, this was not seen for all 5 patients with cervical spondylotic radiculopathy. CONCLUSIONS: The pectoral NCS technique is feasible in healthy subjects. It is useful when differentiating brachial plexopathy from cervical root lesions.

Effect of exercise on repetitive nerve stimulation studies: new appraisal of an old technique.

Repetitive nerve stimulation (RNS) is a simple and rapid method for evaluation of neuromuscular transmission defects. Although the effect of exercise in conjunction with RNS is well recognized, it has not been standardized in actual patient and control groups. In a prospective study over a period of 1 year, the authors evaluated the effect of exercise in conjunction with RNS in comparison with conventional 3-Hz RNS at rest in the clinical setting. Fifty-four patients who were referred for possible neuromuscular transmission disorders, in addition to 35 healthy control subjects, were studied. Amplitude and area decremental responses with RNS at rest and after 20 seconds of maximal exercise at 1-minute intervals up to 3 minutes were evaluated. The use of RNS with exercise resulted in additional diagnostic yield of up to 36.4% compared with conventional 3-Hz RNS at rest. The standardized use of exercise with RNS is advocated for increasing its diagnostic yield in the neurophysiologic laboratory.