Reduction in the motor unit number estimate (MUNE) after cerebral infarction

We examined the relationship between the degree to which motor unit number estimates (MUNEs) decrease in association with the clinical features of patients with the infarction. Using a multiple-point stimulation technique, we obtained the MUNE of the hypothenar muscle group in 13 age-matched control subjects and 30 patients with cerebral infarction. In all patients, we obtained the Japan Stroke Scale (JSS) and head MR images. In 8 patients with acute cerebral infarction, admitted within 24 h after onset, we also obtained head MR angiograms and single-photon emission CT. There was a decrease in the MUNE of the hypothenar muscle group on the affected side of 24 patients with cerebral infarction and hand weakness. The decrease in the MUNE started from 4 to 30 h after the infarction, when T1-weighted MR images of the brain involved were normal. The degree to which the MUNE decreased correlated with the part of the JSS showing the upper extremity weakness. A decrease in the MUNE of the hypothenar muscle group within 30 h after cerebral infarction may be due to transsynaptic inhibition of the spinal alpha motor neurons innervating this muscle.