The physiological functional loss of single thenar motor units in the stroke patients: when does it occur? Does it progress?
OBJECTIVE
We examined the time at which loss of functioning motor units occurs on the hemiparetic side, the relationship between that loss and hemiparetic severity, and how long that loss continues.


METHODS
Sample surface motor unit action potentials (S-MUAPs) were evoked in F-waves. They entirely represent the activity of the relative numbers of different shape S-MUAPs for each abductor pollicis brevis muscle. S-MUAPs from selected population of F-waves were averaged after aligning onset latency. Motor unit number was obtained by dividing the maximum M-potential negative peak amplitude by the averaged S-MUAP one.


RESULTS
The motor unit number on the hemiparetic side was significantly lower than that on the unaffected side in stroke patients who had suffered hemiparesis for more than 9 days. This motor unit loss was greater in patients with severe hemiparesis. One year after onset, the chronic stroke patients showed the same motor unit loss on hemiparetic side as they had 3-4 months after onset.


CONCLUSIONS
Motor unit loss on the hemiparetic side is present as early as the second week after onset and is correlated with hemiparesis severity, and this loss continues out to 1 year. This may be due to trans-synaptic degeneration that occurs secondarily to upper motor neuron lesion.
Hara
Yukihiro
Y
Department of Rehabilitation Medicine, Nippon Medical School, Chiba Hokusoh Hospital, 1715 Kamakari, Inbamura, Inbagun, Chiba Prefecture 270-1694, Japan. hara-y@nms.ac.jp
Masakado
Yoshihisa
Y
Chino
Naoichi
N
D000200:Action Potentials / Q000502:physiology; D002908:Chronic Disease; D018450:Disease Progression; D004576:Electromyography; D004594:Electrophysiology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D032342:Muscle Cells / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology; D010291:Paresis / Q000503:physiopathology; D013116:Spinal Cord / Q000503:physiopathology; D020521:Stroke / Q000503:physiopathology*