The physiological functional loss of single thenar motor units in the stroke patients: when does it occur? Does it progress?

• Published in: Clinical neurophysiology Vol. 115; no. 1; pp. 97 - 103
• Main Authors: Hara, Yukihiro, Masakado, Yoshihisa, Chino, Naoichi
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 2004; Elsevier Science
• Subjects: Action Potentials - physiology; Biological and medical sciences; Chronic Disease; Disease Progression; Electrodiagnosis. Electric activity recording; Electromyogram; Electromyography; Electrophysiology; Evoked Potentials, Motor - physiology; F-wave; Female; Functional Laterality - physiology; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Median Nerve - physiopathology; Medical sciences; Middle Aged; Motor Neurons - physiology; Motor unit; Muscle Cells - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiopathology; Nervous system; Neural Conduction - physiology; Neurology; Paresis - physiopathology; Spinal Cord - physiopathology; Stroke; Stroke - physiopathology; Trans-synaptic degeneration; Vascular diseases and vascular malformations of the nervous system; Electromyogram; Stroke; F-wave; Trans-synaptic degeneration; Motor unit; Human; Hemiparesis; Nervous system diseases; Motor system disorder; Cardiovascular disease; Action potential; Motor neuron; Striated muscle; Electrodiagnosis; Evoked potential; Abductor pollicis brevis muscle; Degeneration; Electromyography; Lesion; Neurological disorder; Cerebrovascular disease; F wave
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2003.08.002

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.