Chizuko Oishi

Decremental responses to repetitive nerve stimulation (RNS) in motor neuron disease.

OBJECTIVE To clarify the features of decremental responses following repetitive nerve stimulation in patients with motor neuron diseases (MNDs), in comparison with myasthenia gravis (MG). METHODS The subjects consisted of 48 MND, 39 generalized MG and 19 ocular MG patients. Six muscles, both proximal and distal muscles, were tested. RESULTS Significant decrements (>5%) in at least one muscle were observed in 83% of the MND patients, and 74% and 47% of the generalized MG and ocular MG patients, respectively. Decrements were more frequently observed in the proximal muscles both in MND and MG patients (deltoid 76% and 62%, and trapezius 71% and 51% for MND and generalized MG, respectively), suggesting lower safety factors in neuromuscular transmission in those muscles. Decrements in the nasalis were rare in MND (8%) in comparison with generalized MG (54%). CONCLUSIONS Decremental responses were frequently observed in MND patients. There were small differences between MND and MG regarding the distribution and other features of decrements, such as the degree of the U-shape or the responses to different stimulus frequencies and to brief exercise. SIGNIFICANCE These results imply that the underlying mechanism regulating the decrements is common to MND and MG.

C8 and T1 innervation of forearm muscles.

OBJECTIVE C8-dominant innervation of ulnar-innervated and T1-dominant innervation of median-innervated intrinsic hand muscles have been suggested, although less is known regarding forearm muscles. We aimed to determine myotomal innervation of the forearm muscles based on the clinical and electromyographial findings of patients with C8 or T1 lesions. METHODS Medical Research Council scale and EMG findings were retrospectively reviewed in 16 patients with C8 lesions (2 postmedian sternotomy C8 plexopathy and 14 C8 radiculopathy) and 9 patients with T1-dominant lesions (8 true neurogenic thoracic outlet syndrome and 1 T1 radiculopathy). RESULTS Clinical and EMG findings revealed T1-dominant innervation of the flexor digitorum superficialis, flexor digitorum profundus of the index finger, abductor pollicis brevis, and flexor pollicis longus muscles, and C8-dominant innervation of the flexor carpi ulnaris, flexor digitorum profundus of the little finger, and digit extensors innervated by the posterior interosseous nerve. The first dorsal interosseous, and abductor digiti minimi muscles seem to be innervated by both C8 and T1 roots. CONCLUSIONS C8-dominant innervation of ulnar-innervated muscles and T1-dominant innervation of median-innervated muscles are also evident for forearm flexor muscles. SIGNIFICANCE Such an additional evidence for myotomal innervation will improve localization in clinical as well as electrophysiological diagnoses.

Guillain-Barré syndrome in two patients with respiratory failure and a review of the Japanese literature

We described two patients with Guillain-Barré syndrome and respiratory failure with or without mechanical ventilation. Case 1 was a 44-year-old man who treated as pneumonia under mechanical ventilation for a month and transferred to our hospital with unsuccessful weaning trials because of phrenic nerve palsy. Case 2 was a 74-year-old man who presented with aspiration pneumonia because of bulbar palsy. The present two cases with review of the Japanese literature showed that antecedent infection with initial symptoms within the most recent 5 to 46 days is a clinical clue to the diagnosis even in patients with Guillain-Barré syndrome accompanied by respiratory failure.

O-2-31. The usefulness of electrophysiological examinations in the diagnosis of tarsal tunnel syndrome

TTS is usually diagnosed based on clinical symptoms and signs, and electrodiagnostic (EDx) tests, typically nerve conduction studies. We aimed to present a case series of TTS and investigate the diagnostic role of EDx. We searched our EMG database from 2008 to 2016 with the keyword of TTS, and retrospectively reviewed clinical and EMG records of extracted patients. The entry criteria were: (1) clinical diagnosis of TTS by the referring doctor, (2) numbness of sole and a positve Tinel’s sign at the ankle, and (3) both the tibial motor conduction study (MCS) and plantar sensory conduction study (SCS) were conducted. Enrolled were 12 patients (20–82 years, 9 men and 3 women). Some EDx tests were abnormal in 8 patients. Plantar SCS was abnormal on the affected side in 5 patients. In 2 of them, tibial MCS showed a bilobed compound muscle action potential (CMAP) indicating the isolated delay of the medial plantar nerve. One patient had abnormal F wave, and 2 patients was shown denervation potentials in the FHB muscle. TTS is in general difficult to confirm electrodiagnostically, although this study supported the role of EDx. Bilobed tibial CMAP may be a previously undescribed sign of TTS.

S79. The utility of tibial nerve SEPs in diagnosing lumbar spinal stenosis, comparison with NCS and F-Waves

Introduction Lumbar spinal stenosis (LSS) is a popular cause of lower limb motor and sensory impairments and gait disturbance. SEPs can be a tool to evaluate LSS, and there have been considerable number of studies investigating the utility of dermatomal SEP in evaluating LSS or lumbar radiculopathy. However, few studies investigated the utility of tibial nerve SEPs. Tibial nerve SEPs have an advantage that they can evaluate plural points along the whole course of the peripheral nerve and can localize the lesion site. Three segments of ankle-knee, knee-pelvis, and pelvis-spinal entry can be evaluated by N8o latency, N8o-P15 interval, and P15-N21 interval. In this study, we compared the utility of tibial nerve SEPs with nerve conduction studies (NCS) and F-waves. Methods We searched our EMG database from 2012 to 2017 with the keyword of “LSS” or “lumbar” and SEP examinations. For extracted cases, we retrospectively reviewed clinical and EMG records and MRI images. The entry criteria were as follows: (1) presence of sensory, motor, or gait (typically, intermittent claucication) complaints, (2) unequivocal LSS in lumbar MRI, (3) final diagnosis that the chief complaint was caused by the MRI-documented LSS, (4) Tibial nerve SEPs, motor conduction study (MCS) and F waves of the tibial nerve, and sensory conduction study (SCS) of the sural nerve were conducted for the same lower-limb that was the more affected, (5) no other causes that can explain his or her symptoms, especially neuropathies and diabetes, (6) no prior lumbar surgery. Results Among 39 patients initially extracted, many have been excluded by the strict inclusion criteria. Finally enrolled were 8 patients (53–82 years, all men). The clinical features of these patients were as follows. Weakness was present in 7 (absent in 1). Sensory symptoms or signs were present in 4 (absent in 4). Intermittent claucication was present in 3 patients. Tibial nerve SEPs were abnormal in 7, and could localize the lesion at the lumbar segment (P15-N21) in 6. Notably, in 3 out of 4 patients without sensory symptoms or signs, tibial nerve SEPs localized the lesion at lumbar segment. The amplitude of the compound muscle action potential (CMAP) of the tibial MCS was reduced in 2 cases, and F-wave latency was prolonged in the same 2 cases. In no cases, F-waves were abnormal despite normal SEPs. Sural SCS was normal for all cases. In two patients in which tibial nerve SEPs could not localize the lesion, needle EMG confirmed the diagnosis of LSS. Conclusion Tibial nerve SEPs are useful in diagnosing LSS by localizing the lesion at the lumbar segments. Especially the fact that they documented lumbar lesions in patients lacking sensory symptoms or signs would contribute to the differentiation from amyotrophic lateral sclerosis. The sensitivity of F-waves was much lower than tibial nerve SEPs and added no value to the amplitude of the tibial CMAP.

A new pitfall in a sensory conduction study of the lateral antebrachial cutaneous nerve: spread to the radial nerve.

Introduction: We describe a previously unreported pitfall, spread of the stimulus at the elbow to the radial nerve, in an antidromic sensory nerve conduction study of the lateral antebrachial cutaneous (LAC) nerve. Methods: Subjects consisted of 80 healthy volunteers, and both sides were examined for each subject. Besides routine recording of the LAC nerve, sensory nerve action potentials (SNAPs) of the radial nerve were recorded distally. Results: The spread phenomenon occurred in 73 of 160 arms (46%), and the SNAP amplitude increased due to contamination of the radial SNAP up to 6.7 times the genuine LAC SNAP. In 10 arms (6%), the spread started before the LAC SNAP was saturated, and the genuine LAC SNAP was unknown due to an anatomical variation in at least 1 arm. Conclusions: Without monitoring distal radial SNAPs, the spread phenomenon will remain unrecognized. This pitfall undermines the reliability of the test. Muscle Nerve 50:186–192, 2014

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.

39. Sensory nerve conduction study normal values of the lateral antebrachial cutaneous nerve

Introduction: Prior to initiating a reaching movement with the arm, an individual must rapidly orient their attention and gaze towards a desired object. In primates, a burst of early electromyographic (EMG) activity occurs in neck muscles prior to the initiation of saccadic eye movement towards a visual target. This early EMG activity primes the motor system, as it increases the reaction time of eye movement towards the target. Objectives: The authors hypothesize that human arm muscles exhibit a burst of early EMG activity prior to the initiation of a reaching movement towards a visual target. Methods: Eight human subjects were positioned in a robotic exoskeleton that recorded right arm kinematics. Subjects performed a reaching task while a continuous intramuscular EMG activity was recorded with fine wire electrodes from the brachioradialis, triceps brachii, anterior deltoid, posterior deltoid, pectoralis major, and supraspinatus. Results: Early EMG activity was found to occur in shoulder girdle muscles prior to the movement onset. A burst of EMG activity (20 ms duration) took place 85–105 ms after the target presentation, but 100 ms prior to the movement onset in the anterior deltoid and pectoralis major muscles during shoulder flexion and in the posterior deltoid and the supraspinatus during shoulder extension. Conclusions: Early EMG activity may reflect an important priming of the arm that increases reaction time or accuracy during reaching. Evidence to suggest that orientation to a visual stimulus causes an early EMG activity which is not associated with movement is novel, and has never before been documented. These results have a significant impact on the understanding of the motor system and its relationship to the visual system. L.L. Boisse is a Junior Member Recognition Award Recipient.

51. A pitfall in sensory conduction study of the lateral antebrachial cutaneous nerve (LAC): Spread to the median nerve

333 Hz) while performing weak isometric contraction of the upper limb muscles. Cutaneous reflexes were recorded while the leg was at rest, performing pedaling, isometric contraction of the knee extensors and a one shot-like discrete pedaling motion. The magnitude of the cutaneous reflex in the flexor carpi radialis (FCR), biceps brachii and posterior deltoid (PD) was significantly modulated during leg pedaling compared to that during rest. Modulation of cutaneous reflexes in the FCR and PD strongly depended on the level of isometric contraction of the muscles tested and cadence of pedaling, but did not depend on the pedaling phase or contraction level of the knee extensors. Moreover, cutaneous reflexes were not significantly modulated by discrete leg pedaling. These findings suggest that activity of the rhythm generating system in the spinal cord would affect the excitability of cutaneous reflex pathways in the upper limbs.