The speed of completion of the decremental responses on repetitive nerve stimulation.

Objective: It is generally believed that the decremental response in repetitive nerve stimulation (RNS) stabilizes at the fourth or fifth response. We have a preliminary impression that the decremental response approaches a plateau earlier in proximal muscles than in distal muscles. We investigated the speed of the completion of the decremental response in different muscles. Methods: The "decrement completion ratio (DCR)" in the second or third response (DCR2 or DCR3) was defined as the ratio of the decremental percentage of the second or third response to that of the fourth response. Patients showing more than 10% decremental response both in the abductor pollicis (APB) and deltoid muscles were retrospectively extracted from our EMG database. The DCR2 and DCR3 were compared between two muscles in patients with myasthenia gravis (MG) and amyotrophic lateral sclerosis (ALS). Results: Identified subjects consisted of 11patients with MG and 11 patients with ALS. Multiple regression analysis revealed that only the difference of muscle influenced on DCR2 and DCR3, with no contribution from the different disorder (MG or ALS) or the initial amplitude of the compound muscle action potential (CMAP). Both DCR2 and DCR3 were significantly higher in deltoid than in APB. In ALS, the normalized CMAP amplitude was not different between APB and deltoid whereas the decremental percentage was significantly higher in deltoid, suggesting a lower safety factor of the neuromuscular transmission in proximal muscles. Conclusions: The decremental response completed more rapidly in deltoid than in APB which may be related to the lower safety factor also documented by this study. Significance: Unexpected early completion of the decrement such as at the second response in RNS is not a technical error but may be an extreme of the rapid completion in deltoid, a proximal muscle.

Utility of the Repetitive Nerve Stimulation Test and Needle EMG in the Trapezius Muscle for the Early Diagnosis of ALS.

OBJECTIVES: To document the utility of decremental responses in the repetitive nerve stimulation test (RNS) and spontaneous activities in needle electromyography (EMG) in the trapezius muscle for the diagnosis of amyotrophic lateral sclerosis. METHODS: Subjects were retrospectively identified from our EMG database. Cervical spondylosis was represented as a disease control group. We investigated the sensitivity and specificity of RNS and EMG in the trapezius muscle and those of diagnostic criteria including the Gold Coast criteria (GCC). RESULTS: We reviewed 120 patients with amyotrophic lateral sclerosis and 17 patients with cervical spondylosis. "RNS or EMG" achieved the highest sensitivity (85%). The specificity was the highest for RNS (94%). Addition of RNS of the deltoid muscle achieved 98% sensitivity in the upper-limb onset amyotrophic lateral sclerosis. The sensitivity of the GCC was very high (88%). CONCLUSIONS: Neurophysiological parameters investigated in this study having close to 100% specificities or sensitivities are useful as complements to the GCC.

[A case of acute bilateral blindness presumably caused by reversible cerebral vasoconstriction syndrome after traumatic brain injury].

A 62-year-old man was admitted to our hospital for acute bilateral blindness two days after a head injury. Hemorrhagic cerebellar infarction was found on the initial MRI, and peripheral arteries were poorly visualized on MRA. On the follow-up MRA nine days later, peripheral arteries were clearly depicted. These imaging findings suggested reversible cerebral vasoconstriction syndrome (RCVS). We started steroid pulse therapy for suspected optic neuritis with no clear response. The initial fundoscopic examination revealed no abnormalities in the optic disc, but optic nerve atrophy developed one month later. Based on the course of events, we diagnosed the patient with posterior ischemic optic neuropathy triggered by RCVS.

Weak shoulder and arm sparing signs in amyotrophic lateral sclerosis.

INTRODUCTION/AIMS: Various signs of selective involvement have been reported in amyotrophic lateral sclerosis (ALS). In this study, we describe two new signs, "weak shoulder" and "arm sparing" signs. METHODS: Subjects were retrospectively identified from our electrodiagnosis database. Medical Research Council scores of relevant muscles were evaluated. Weak shoulder was defined as the deltoid (Del) muscle being weaker than the biceps brachii (BB)/triceps brachii (TB) muscles; that is, Del was weaker than either or both of the muscles and no stronger than either. Arm sparing was defined as both Del and the first dorsal interosseous (FDI) being weaker than BB/TB. Sensitivities of these signs were compared with other signs of selective involvement. The specificities of these signs were investigated in patients with cervical spondylotic amyotrophy (CSA) and multifocal motor neuropathy (MMN). RESULTS: We reviewed 130 patients with ALS, 64 patients with CSA, and 16 patients with MMN. The weak shoulder and the arm sparing signs were observed in 73% and 55% of patients with ALS, 44% and 2% of patients with CSA (93% and 0% of patients with proximal CSA), respectively, and no patients with MMN. The sensitivity of the weak shoulder was higher than with conventional signs, whereas that of the arm sparing sign showed no difference. DISCUSSION: The weak shoulder sign was highly sensitive in ALS, and was specific when compared with MMN. The arm sparing sign was highly specific for ALS. These two new signs are promising as clinical clues in the diagnosis of ALS.

The influence of right-left error in the placement of the Cc electrode in tibial nerve somatosensory evoked potentials (SEPs).

OBJECTIVE: At our laboratory, we routinely record tibial nerve somatosensory evoked potentials (SEPs) using 5 channels including the second cervical vertebra (C2S)-contralateral central area (Cc) and Cz' (2 cm posterior to Cz)-Cc derivations. In a man with lumbar spondylotic myelopathy, symptoms improved after surgery, although the N21-P38 interval was markedly prolonged in comparison with that before surgery. We presumed that the Cc electrode was actually placed on the ipsilateral central area (Ci) at the second examination. Inspired by this episode, we investigated the influence of the right-left error in the placement of the Cc electrode. METHODS: Subjects were 20 healthy volunteers. Tibial nerve SEPs were recorded with 8 leads including Cz'-Cc, Cz'-Ci, C2S-Cc and C2S-Ci. RESULTS: For the Cz'-Ci lead, the P38 potential diminished in amplitude, was absent or became negative. For the C2S-Ci lead, a large negative potential corresponding to the phase reversal of P38 was frequently observed. CONCLUSIONS: Tibial nerve SEPs using the Cz'-Cc or C2S-Cc lead are distorted if the Cc electrode is placed on the opposite side. SIGNIFICANCE: When a strange result is obtained in tibial nerve SEPs, we should check for a right-left error in the Cc electrode placement.

Aquaporin-4-antibody-positive Neuromyelitis Optica Spectrum Disorder in a Patient with Charcot-Marie-Tooth Disease Type 1A.

Charcot-Marie-Tooth disease type 1A (CMT1A) is a hereditary peripheral neuropathy, and its involvement in the central nervous system (CNS) is very rare. We herein report a 51-year-old woman with CMT1A who suffered from recurrent optic neuritis and myelopathy. Under the diagnosis of anti-aquaporin-4 (anti-AQP4) antibody positive neuromyelitis optica spectrum disorder (NMOSD), we treated her successfully with corticosteroids. This is the first report of CMT1A complicated with anti-AQP4-positive NMOSD. Although the coexistence of the two disorders may simply be a coincidence, we speculated that immune cross-reaction between overexpressed peripheral myelin protein 22 and CNS myelin may have caused concomitant CMT1A and NMOSD.

[Severe sensory-motor axonal neuropathy following diabetic ketoacidosis].

We report a case of severe sensory-motor axonal neuropathy on the lower extremities associated with diabetic ketoacidosis (DKA). A sixteen-year-old boy developed coma and admitted to our hospital. We diagnosed him with DKA based on remarkable hyperglycemia, severe acidosis with hyperketonemia. Intensive glycemic control with insulin was immediately started. He had complications of heart failure, rhabdomyolysis, and renal failure, which required intensive care including mechanical ventilation and hemodialysis. When recovered from the critical condition, he noticed severe weakness, numbness, and pain on the lower limbs, and urinary retention. On nerve conduction studies, both motor and sensory action potentials were absent. Serum anti-ganglioside antibodies were negative. Albuminocytologic dissociation was evident in the cerebrospinal fluid. MRI study revealed marked gadolinium enhancement of the cauda equina. After high-dose intravenous immunoglobulin treatment, he was relieved from leg pain, but the leg weakness and bladder bowel dysfunction did not show immediate improvement. It took approximately six months until he became able to stand and walk using ankle orthosis. Acute neuropathy is a rare complication of diabetes mellitus. Painful neuropathy is known to emerge in association with diabetic treatment, but it seldom causes severe motor disturbance. On the other hand, motor-dominant polyneuropathy has been reported to occur acutely along the treatment of DKA and hyperosmolar hyperglycemia syndrome (HHS). Present case and previous cases with DKA and HHS suggest that rapid correction of glucose level is one of the underlying factors of acute neuropathy related with diabetic treatment.

Microelectrode mapping of tonotopic, laminar, and field-specific organization of thalamo-cortical pathway in rat.

The rat has long been considered an important model system for studying neural mechanisms of auditory perception and learning, and particularly mechanisms involving auditory thalamo-cortical processing. However, the functional topography of the auditory thalamus, or medial geniculate body (MGB) has not yet been fully characterized in the rat, and the anatomically-defined features of field-specific, layer-specific and tonotopic thalamo-cortical projections have never been confirmed electrophysiologically. In the present study, we have established a novel technique for recording simultaneously from a surface microelectrode array on the auditory cortex, and a depth electrode array across auditory cortical layers and within the MGB, and characterized the rat MGB and thalamo-cortical projections under isoflurane anesthesia. We revealed that the ventral division of the MGB (MGv) exhibited a low-high-low CF gradient and long-short-long latency gradient along the dorsolateral-to-ventromedial axis, suggesting that the rat MGv is divided into two subdivisions. We also demonstrated that microstimulation in the MGv elicited cortical activation in layer-specific, region-specific and tonotopically organized manners. To our knowledge, the present study has provided the first and most compelling electrophysiological confirmation of the anatomical organization of the primary thalamo-cortical pathway in the rat, setting the groundwork for further investigation.