ELSEVIER Electroencephalography and clinical Neurophysiology 97 (1995) 73-76 o Central motor conduction in Hirayama disease U.K. Misra *, J. Kalita Department of Neurology, Sanjay Gandhi PostgraduateInstitute of Medical Sciences, Lucknow 226 014, India Accepted for publication: 29 August 1994 Abstract The pathogenesis of Hirayama disease is usually attributed to microcirculatory disturbances in the anterior spinal artery territory, leading to segmental anterior horn cell loss and occasional lower limb hyperreflexia. In 7 patients with Hirayama disease, central motor conduction to upper (CMCT-ADM) and lower limbs (CMCT-TA) was evaluated. CMCT-TA was normal in all, but CMCT-ADM was marginally prolonged (8.4 msec, amplitude 0.8 mV) on one side only. Peripheral delay in the upper limbs was found in 2 patients (1 side each) which might be due to fall-out of anterior horn cells. In 2 patients with lower limb hyperreflexia, HM ratio, vibratory inhibition and reciprocal inhibition of soleus H reflex were also normal, suggesting lack of pyramidal dysfunction. Our results do not suggest any pyramidal dysfunction as a cause of lower limb hyperreflexia in Hirayama disease. Keywords: Spinal muscular atrophy; Motor pathways; Pyramidal signs Non-progressive juvenile spinal muscular atrophy of the distal muscles has been reported mainly from Japan but also from Denmark, Holland, Singapore, USA, India, Malaysia, Sri Lanka and France (Hirayama 1972, 1991; Sobue et al. 1978). Its aetiology is not well understood but has been attributed by some to microcirculatory distur- bances in the territory of the anterior spinal artery (Hirayama 1991). MRI of these patients has revealed high intensity in T1 and T2 weighted spin echo sequences (Mukai et al. 1987) which is consistent with congestion of the epidural venous plexus. Vulnerability of anterior horn cells to ischaemia is consistent with segmental atrophy; it may also be associated with abnormalities in cortico-spinal tracts, which are located in the watershed zone. Rarely lower limb hyperreflexia has been reported in Hirayama disease which is consistent with pyramidal tract dysfunc- tion (Hirayama 1991). The motor dysfunction in these patients has not been objectively documented. The present study, therefore, has been undertaken to evaluate the cen- tral motor conduction in Hirayama disease. * Corresponding author. I. Patients and methods Seven patients with Hirayama disease were included in this study. The diagnostic criteria (Hirayama 1991) in- cluded: (1) Occurrence in males of 15-25 years. (2) Insidious onset of unilateral or asymmetric oblique amyotropy, often associated with cold paresis. (3) Association with fine tremulous irregular involun- tary movements of the fingers on moderate extension or fasciculation in the extensors of the forearm. (4) Absence of sensory findings, reflex changes in arms, little if any pyramidal signs in the leg, ocular or sphincter disturbances. (5) Non-progressive course, arrest within few years after the onset. (6) Laboratory data: neurogenic changes in EMG and muscle biopsy restricted to C7, C8 and T1 myotomes; normal nerve conduction studies and atrophy of lower cervical spinal cord with forward displacement of lower cervical dural canal on neck flexion. Motor nerve conduction velocities of median, ulnar and peroneal nerves were measured and proximal stimulation was done in all the patients to study conduction blocks. Sensory conduction velocities of median, ulnar and sural 0924-980X/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0013-4694(94)00246-0 EEM 94503