T.H. Leoh

Repetitive hypoglossal nerve stimulation in myasthenia gravis.

OBJECTIVES To assess the diagnostic efficacy of repetitive nerve stimulation (RNS) of the hypoglossal nerve in patients with myasthenia gravis (MG) and bulbar symptoms (dysphagia, dysarthria). METHODS Twenty patients with MG and 25 normal controls had RNS of the hypoglossal nerve. All patients also had single fibre electromyography (SFEMG) of the orbicularis oculi and RNS with recordings of the nasalis, trapezius and abductor pollicis brevis muscles. RESULTS All patients had positive SFEMG studies. Nine patients with bulbar symptoms had positive hypoglossal RNS, including 3 with negative RNS recordings in other muscles. Eleven patients with no bulbar symptoms showed negative hypoglossal RNS, including two with positive RNS recordings from other muscles. CONCLUSIONS Abnormal RNS of the hypoglossal nerve correlates well with bulbar dysfunction and further characterises the extent of neuromuscular transmission defect in MG patients.

Decrement in area of muscle responses to repetitive nerve stimulation

Measurement of the decremental muscle response to repetitive nerve stimulation (RNS) has low yields for the diagnosis of neuromuscular transmission defects compared with single fiber electromyography (SFEMG). We compared area and amplitude of muscle responses to RNS in 87 patients and 30 controls, using SFEMG as the reference standard. Decrement of response area provided additional diagnostic yields of 5.3% to 30% depending on the muscle examined and disease severity, and is recommended as a diagnostic adjunct to measurement of amplitude decrement during RNS. Muscle Nerve 27: 494–496, 2003

Clinical and electrophysiological aspects of distal ulnar neuropathy

Objectives– To evaluate the use of fixed distance side to side comparison of abductor digiti minimi (ADM) and first dorsal interosseous (FDI) compound muscle action potential (CMAP) studies in the diagnosis of distal ulnar neuropthy. Materials and methods– Thirty normal controls underwent ADM and FDI CMAP studies bilaterally at a fixed ADM recording to stimulating point distance of 6 cm. Side to side mean latency differences to both muscles were calculated. Twenty patients with suspected unilateral distal ulnar neuropathy from routine nerve conduction studies had positive results when compared with controls. Results– The upper limit of normal for side to side mean latency difference at 3 SD above the mean was 0.394 and 0.474 ms for ADM and FDI, respectively. All 20 patients had side to side mean CMAP latency difference above 3 SDs in the ADM, FDI or both muscles. Fifty percent of cases had involvement of the superficial sensory branch. Conclusions– Fixed distance side to side CMAP latency comparison is a useful electrodiagnostic adjunct for distal ulnar neuropathy. Trauma was the most common aetiology in the 20 reported cases. Correlation was found between aetiological factors and sites of lesions as localized with this method.

Rapid ultrasonographic diagnosis of radial entrapment neuropathy at the spiral groove

BACKGROUND Entrapment neuropathy of the radial nerve at the spiral groove region is relatively common. However, its localization may be technically challenging. OBJECTIVE To evaluate the use of ultrasound (US), in relation to electrophysiological testing, for this purpose. METHODS We studied 32 normal controls to obtain US parameters of the radial nerve. In addition, 10 patients with suspected radial neuropathy were tested using US and electrophysiological techniques. RESULTS US examination correctly identified all 6 patients with radial neuropathy. The other 4 patients with alternate diagnoses did not show US abnormalities exceeding that of normal controls. US examination required a significantly shorter time than electrophysiological testing. CONCLUSIONS US is of value as a rapid diagnostic adjunct for the localization of radial nerve entrapment.

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.

Superficial peroneal sensory and sural nerve conduction studies in peripheral neuropathy

The objective of this study was to prospectively evaluate sensory nerve conduction studies (NCS) in the distal lower limbs in the electrodiagnosis of peripheral neuropathy. We prospectively studied 316 consecutive patients with surface stimulation and recording, in comparison with 90 control subjects. A total of 310 patients were found to have lower limb sensory NCS abnormalities. In these patients, the rate of detection of peripheral neuropathy with superficial peroneal NCS (88.5%) was significantly higher (P<0.001) compared with sural NCS (75%). The superficial peroneal NCS appeared to have a higher detection rate for peripheral neuropathy in our study, and its study can be adjunctive to sural NCS.

High-resolution ultrasound in the evaluation and prognosis of Bell's palsy.

Introduction:  Bell’s palsy is a commonly encountered paralysis of the facial nerve occurring worldwide. Prognosis for Bell’s palsy is good, but the proportion of patients with poor outcomes may reach 30%. Ultrasound (US) may provide a novel approach for evaluating and prognosticating Bell’s palsy, in comparison with known electrophysiological techniques.

Cutaneous silent periods in the evaluation of cord compression in cervical spondylosis

ObjectiveThe clinical diagnosis of cervical spondylotic myelopathy (CSM) may be challenging in patients with cervical spondylosis (CS). Routine nerve conduction studies (NCS) may not evaluate cord compression adequately.MethodsWe obtained cutaneous silent periods (CSP) in 26 consecutive patients presenting with clinical features of CS, in comparison with 30 normal controls. The results were also compared with transcranial magnetic stimulation (TMS) findings, and magnetic resonance imaging of the cervical cord as the gold standard.ResultsCSP findings showed similarly high sensitivity of up to 96% with TMS in evaluating cervical cord dysfunction.ConclusionIn specific clinical settings, CSP is of value for the diagnosis of CSM in CS. CSP measurement is advocated as a simple and rapid diagnostic adjunct to NCS in evaluating CS patients with possible cord compromise.

Short-segment nerve conduction studies in the localization of ulnar neuropathy of the elbow : Use of flexor carpi ulnaris recordings

Short‐segment nerve conduction studies were performed in 17 limbs with clinical features suggestive of ulnar neuropathy at the elbow. Recording from flexor carpi ulnaris yielded 93% sensitivity, compared with 71.4% when recording from abductor digiti minimi. The rationale underlying the technique is discussed. This approach should be of value as a diagnostic adjunct in technically challenging cases of ulnar neuropathy at the elbow. Muscle Nerve, 2005

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.