Y. Hatanaka

Single fiber EMG and repetitive nerve stimulation of the same extensor digitorum communis muscle in myasthenia gravis.

OBJECTIVE To compare voluntary single fiber electromyography (v-SFEMG) and repetitive nerve stimulation (RNS) at the same extensor digitorum communis (EDC) muscle in myasthenia gravis (MG). METHODS We examined v-SFEMG and RNS successively on the same day in the same EDC muscle. We studied 45 examinations of both v-SFEMG and RNS in 29 patients suffering from MG, together with examinations of RNS in 30 control subjects. RESULTS Forty-one of 45 (91%) v-SFEMGs showed abnormal results, whereas only 18/45 (40%) RNSs showed an abnormal decrement. The percentage of decrement showed similar correlations with 3 v-SFEMG parameters: percentage of abnormal pairs, percentage of blocking pairs, and the mean MCD value. Examinations showing a significant decrement in RNS had at least 60%, and usually no less than 90%, abnormal pairs, and 10-80% blocking pairs. Some muscles without a decrement had up to 50% blocking pairs. CONCLUSIONS These results suggest that the blocking phenomenon observed in v-SFEMG is not a direct counterpart of the decrement in RNS. This must be partly because fibers contributing to the decrement are continuously blocked during voluntary contraction, and partly, because smaller motor units explored by v-SFEMG are probably more abnormal in MG than larger motor units mainly contributing to a decrement. Both factors make v-SFEMG much more sensitive than RNS.

N18 in median somatosensory evoked potentials: a new indicator of medullary function useful for the diagnosis of brain death

OBJECTIVES To record N18 in median somatosensory evoked potentials (SEPs) for deeply comatose or brain dead patients and to demonstrate the usefulness of N18 for the diagnosis of brain death in comparison with auditory brain stem responses (ABRs) and P13/14 in median SEPs, which have been conventionally used as complementary tests for the diagnosis of brain death. METHODS Subjects were 19 deeply comatose or brain dead patients. Thirteen recordings were performed in deeply comatose but not brain dead conditions, and 12 recordings were performed in brain death. N18 was evaluated in the CPi-C2S lead (or other scalp-C2S leads) to obtain a flat baseline. RESULTS N18 was preserved in 12 of 13 non-brain dead comatose recordings whereas it was completely lost for all of the 12 brain death recordings. P13/14 in median SEPs was preserved for all the comatose recordings, whereas apparent P13/14-like potentials, usually of low amplitude, were seen in nine of 12 brain death recordings—that is, frequent false positives. The ABRs already showed features which were characteristic for brain death (loss of components other than wave 1 or small wave 2) for four comatose recordings, in three of which N18 was preserved. The last result not only corresponds with the fact that ABRs can evaluate pontine and midbrain functions and not medullary function, but further supports the medullary origin of N18. In the four patients followed up for the course of progression from coma to brain death, N18s preserved in normal size during the comatose state were completely lost after brain death was established. CONCLUSIONS The N18 potential is generated by the cuneate nucleus in the medulla oblongata in the preceding studies. N18 is suggested to be a promising tool for the diagnosis of brain death because there were no false positives and rare false negatives in the present series for detecting the remaining brain stem function.

A common mutation and a novel mutation in Japanese patients with van der Knaap disease.

AbstractVan der Knaap disease, or megalencephalic leukoencephalopathy with subcortical cysts (MLC), is an autosomal recessive disorder clinically characterized by macrocephaly, ataxia, spasticity, and mental decline. Magnetic resonance imaging (MRI) shows swollen brain with diffuse white-matter abnormalities and subcortical cysts, particularly in the anterior-temporal region. Recently, the MLC1 gene was identified as the gene responsible for this disorder, and mutations in this gene were described in several patients. We studied three Japanese patients with van der Knaap disease at the molecular genetic level. Two of them were homozygous for a previously-described mutation, S93L, and one was a compound heterozygote for S93L and a novel mutation, 452-468del+g, which leads to frameshift with a premature termination codon. Combining our data with previous reports allowed us to estimate the molecular genetic basis of this disorder in seven Japanese patients. In summary, S93L was observed in six of seven (85.7%) patients at least in one allele, and ten of 14 (71.4%) alleles had this mutation. Therefore, S93L appears to be fairly frequent in Japanese patients with van der Knaap disease, and analysis for this mutation in DNA isolated from leukocytes would provide for an easy and precise diagnosis of this disorder in Japanese patients.

Spread of the radial SNAP: A pitfall in the diagnosis of carpal tunnel syndrome using standard orthodromic sensory conduction study

OBJECTIVE To investigate the occurrence of the spread of the radial sensory nerve action potential (SNAP) among patients with carpal tunnel syndrome (CTS) during standard median orthodromic sensory conduction study (SCS) using index finger stimulation. METHODS We prospectively examined 74 hands in 56 CTS patients. We stimulated the index finger using ring electrodes. SNAPs were recorded at wrist over median and radial nerves. RESULTS A spread of radial SNAP was clearly identified over the median nerve despite its small amplitude, in 72/74 hands during stimulation of the base of the index finger. In hands with delayed median SNAP, two peaks were observed; however in hands with absence of genuine median SNAP, only one peak of the spread was noticed. The proximal interphalangeal joint (PIP) stimulation still elicited an identifiable spread in 47/74 hands. CONCLUSION This spread phenomenon is a previously undescribed pitfall during the standard median orthodromic SCS, frequently occurring in CTS patients. SIGNIFICANCE In severe CTS cases, one may make wrong conclusion of normal median sensory latency if unaware of this pitfall.

N10 component in median nerve somatosensory evoked potentials (SEPs) is not an antidromic motor potential.

OBJECTIVE To test the hypothesis that the N10 far-field potential in median nerve somatosensory evoked potentials is generated by the motor axons by examining patients with amyotrophic lateral sclerosis (ALS). METHODS Subjects were 5 ALS patients showing pronounced or complete denervation of median-innervated small hand muscles. We evaluated N10 over scalp, and proximal plexus volleys (PPVs) at lateral or anterior cervical electrode. RESULTS N10 and PPVs were definitely preserved for every ALS subject. N10 amplitudes of ALS subjects were even significantly larger than control subjects. In one ALS patient completely lacking motor axons, N10 was larger than the largest one among control subjects. CONCLUSIONS Present results clearly indicate that N10 is not predominantly generated by motor axons but by the whole median nerve dominated by sensory axons. We propose a theory that N10 is a junctional potential generated by the entrance of the median nerve into bone at the intervertebral foramen, producing a positive pole at the non-cephalic reference electrode. Significantly larger N10 in ALS subjects may be due to the lack of cancellation by slower motor axons. SIGNIFICANCE The hypothesis that N10 is generated by motor axons is refuted, and a new theory of its generation is presented.

P5.7 Activity dependent conduction block and distal conduction disturbance after exercise in anti-MAG neuropathy

Methods: We retrospectively reviewed clinical, electrophysiological and MRI findings of two CIDP patients. Results: Quadriparesis predominating in lower extremities began 3 weeks ago in the 33-year-old female and 10 days before in the 58 years-old male patient. Both showed albuminocytological dissociation on cerebrospinal fluid examination. Although nerve conduction studies did not reveal any demiyelinating findings, needle EMG showed reduced recruitment. Lower extremity somatosensorial evoked potentials (SEP) could not be recorded in both patients. Spinal MRI of both patients demonstrated thickened and marked enhancement of lumbosacral nerve roots. They received 0.4 gr/kg/day dose intravenous immunoglobulin (IVIG) for 5 days. Progression halted only for ten days and began again in the first patient. A second dosing of IVIG was ineffective and progression continued. The second patient showed a partial improvement for 7 months, followed by two exacerbations in three months. 1 mg/kg oral prednisolone was started in both patients and followed by almost complete recovery in six months. Conclusion: In spite of normal nerve conduction studies, exacerbations after onset of symptoms, or ongoing progression over at least two months, albuminocytological dissociation and nerve root enhancement on spinal MRI should suggest treatable polyneuropathies, like CIDP.

P21-26 Distal conduction disturbance after post exercise in anti-MAG neuropathy

are compatible with prolonged action potential and delay repolarization in traditional neurophysiological study. One of the patients suffered from severe cramp in hands especially in the winter and difficulty in writing and housework, others are no obvious problems in daily activities. The recovery cycles test on this patient showed prominently increasing in superexcitabilities and prolonged period of superexciability. Conclusion: Nerve excitability tests might contribute the direct of indirect information about ion channel function, including nerve and muscle.

P14-6 Utility of somatosensory evoked potential (SEPs) for the diagnosis of sensory CIDP

(64vs. 128-channels) and stimulation of four distal sites in the upper limbs (the 1st and the 5th digit, the superficial branch of the radial nerve and the ulnar nerve). After choosing the best couple of stimulation sites to assess the cortical representation of the hand, we tested the possible plastic effect of rTMS on the hand cortical representation in 5 subjects. The most robust separation of somatosensory sources was achieved by comparing the cortical representations of the 1st digit and the distal ulnar nerve territories using the N20/P20 component of SEPs with both range of spatial sampling but only the 128-electrodes montage was able to significantly separate sources in the other cases. Reliable distinction of cortical representations was not obtained using the P45 component. In the 5 subjects analyzed so far, the localization of SEP sources in the primary sensory area changed after rTMS, but changes were not correlated with sensory modifications on clinical examination. Assessment of tangential SEP components to stimulation of 1st digit vs. ulnar nerve appears the best option to assess cortical somatosensory plasticity, especially if a relatively low electrode sampling is used. Preliminary results obtained after a rTMS session suggest a possible modification of the cortical somatotopic representation of the hand.

38. Origin of the far-field potentials in radial motor conduction study

RNS at 2, 5, 10, and 20 Hz was determined by two blinded investigators using defined criteria (baseline return of >80 ms) in 45 patients (19 normal, 20 PN, and 6 PNH). Results: The median afterdischarge durations were similar among the 3 groups of patients. However, the 75th percentile of the afterdischarge durations at 2, 5, 10, and 20 Hz were higher for PNH patients than controls and PN patients (323, 751, 792, and 959 ms for normal controls; 117, 42, 354, 563 ms for PN patients; 941, 1617, 1794, 1298 for PNH patients). Conclusions: Although there may be some differences between the three groups in distributions of afterdischarge durations, they overlap considerably. This would suggest that aftercharge durations are unlikely to be useful in the diagnosis of PNH syndromes. Cynthia L. Bodkin, MD, Junior Member Recognition Award.