Central motor conduction in Hirayama disease.

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.