Utility of repetitive nerve stimulation test for ALS diagnosis.

OBJECTIVE: Decremental responses in the repetitive nerve stimulation (RNS) test in amyotrophic lateral sclerosis (ALS) patients have been reported, although their possible diagnostic role has received little investigation. We investigated their diagnostic role in differentiation between ALS and cervical spondylotic amyotrophy (CSA), an important ALS mimic especially in Japan. METHODS: Patients were prospectively enrolled and the diagnosis was confirmed by follow-up. RNS was performed on the abductor pollicis brevis (APB), upper trapezius (trapezius) and deltoid muscles. RESULTS: Enrolled subjects consisted of 53 ALS and 37 CSA patients. Abnormal decremental responses (>5%) were observed in 32%, 51% and 75% of ALS patients and 3%, 0% and 20% of CSA patients for the APB, trapezius and deltoid muscles, respectively. The sensitivity for 23 ALS patients with upper-limb onset was 78% for the trapezius and 100% for the deltoid muscles. CONCLUSIONS: An abnormal decremental response in the trapezius muscle was 100% specific to ALS in comparison with CSA: abnormal decrement in this muscle would strongly suggest ALS. No decrement in the deltoid muscle might exclude ALS in patients having symptoms with upper-limb onset. SIGNIFICANCE: RNS is useful in differentiation between ALS and CSA.

Far-field potentials in hypothenar motor unit number estimation.

INTRODUCTION: Contamination by far-field potentials (FFPs) may interfere with motor unit number estimation (MUNE) in the ulnar nerve. METHODS: Surface motor unit potentials (SMUPs) from 29 spinal and bulbar muscular atrophy (SBMA) patients and 27 control subjects were classified into SMUPs from the abductor digiti minimi muscle (ADM SMUPs) or non-ADM SMUPs, based on the waveform patterns from 3-channel recordings. RESULTS: The mean areas of the ADM SMUPs and non-ADM SMUPs in control subjects were 219.0 ± 131.3 and 63.7 ± 48.5 µVms, respectively. In SBMA patients they were 1988.9 ± 999.4 and 222.7 ± 125.7 µVms, respectively. The percentages of non-ADM SMUPs were 68 ± 22% in controls and 84 ± 15% in SBMA patients. CONCLUSIONS: Non-ADM SMUPs generated mainly by FFPs often had a negative onset in the routine lead and were indistinguishable from ADM SMUPs. More frequent exclusion of smaller non-ADM SMUPs in controls by size criteria would reduce the diagnostic yield of MUNE.

Origin of surface motor unit potentials in hypothenar motor unit number estimation.

INTRODUCTION: Far-field potentials (FFPs) from muscles other than the abductor digiti minimi (ADM) may interfere with motor unit number estimation (MUNE) from that muscle. METHODS: We identified the origin of each surface motor unit potential (SMUP) during hypothenar MUNE using the multiple point stimulation method in 20 control subjects by recording from individual ulnar-innervated muscles with a common proximal reference (pref). RESULTS: ADM SMUPs comprised 39.0% of the accepted SMUPs, followed by those from the fourth dorsal interosseous muscle (14.0%), the fourth lumbrical muscle (9.2%), and the second and third palmar interosseous muscles (8.8% each). The percentage of ADM SMUPs varied from 18% to 73% of accepted SMUPs among individual subjects. Accepted non-ADM SMUPs were usually much smaller than ADM SMUPs, and many more non-ADM SMUPs were excluded due to their small size. CONCLUSIONS: A large contribution from non-ADM or non-hypothenar SMUPs obscures the meaning of the MUNE value.

Spread to the dorsal ulnar cutaneous branch: a pitfall during the routine antidromic sensory nerve conduction study of the ulnar nerve.

OBJECTIVE: To document the incidence and effects of a previously unreported pitfall during routine antidromic sensory nerve conduction study (SCS) of the ulnar nerve: the spread of the wrist stimulation to the dorsal ulnar cutaneous (DUC) branch. METHODS: The subjects consisted of 20 healthy volunteers. An antidromic sensory nerve action potential (SNAP) was recorded over the proximal interphalangeal joint of the little finger, and the DUC response was monitored over the dorsum of hand to check for the occurrence of this spread. RESULTS: The spread occurred in all subjects, which caused a 4-87% increase in the SNAP amplitude. The likelihood that this spread may occur during routine SCS varied among the subjects, and also within an individual subject depending on minute shifts of the stimulating site. Selective stimulation of the ulnar main trunk up to maximal intensity without spread to the DUC was not achieved despite every effort in two subjects. CONCLUSIONS: This spread phenomenon may occur frequently during routine antidromic SCS, but would not be recognized without monitoring the DUC response. SIGNIFICANCE: This pitfall may interfere with the reproducibility of the SNAP amplitude, and also with the diagnosis of ulnar neuropathy at the wrist.

[Clinical features of predominantly sensory stroke due to brainstem infarction].

We report 13 patients presenting with predominantly sensory strokes due to brainstem infarction, without any other brainstem symptoms such as hemiparesis, dysarthria or vertigo. All of them had lacunar infarctions localized at the medial lemniscus and/or spinothalamic tract, at the pontine (12 patients) or midbrain (1 patient) tegmentum. The presenting symptom was dysesthesia with a variety of distributions for all cases, and a thalamic-pain-like unpleasant dysesthesia persisted in 4 patients. The lesion on brain MRI was usually very small, and was sometimes overlooked by radiological evaluation, which led to a long delay in the correct diagnosis of a stroke in two cases. Median nerve somatosensory evoked potentials showed a depressed N20 amplitude or a loss of the P15 potential unilaterally with preserved P13/14 potential in 7 out of 10 cases examined, and was useful in localizing the lesion intracranially. During the 4-year study period, 10 patients with brainstem infarctions were admitted to our department as acute sensory stroke cases (2.1% of all acute strokes), whereas 11 patients with thalamic infarctions (2.3%) were admitted due to similar symptoms. Cases with brainstem infarctions had sensory symptoms localized below the neck more frequently (5/10) than cases with thalamic infarctions (1/11), thus would be more likely to be confused with cervical or peripheral nerve disorders. The relative frequency of brainstem infarction as compared to thalamic infarction was higher than that in previous reports, implying that some cases with brainstem infarction might have been overlooked due to difficulty in obtaining the correct diagnosis. One should always keep this syndrome in mind when assessing patients with acute-onset sensory symptoms.