Abnormal spontaneous muscle activity in plegic limb appears to initiate distal to the upper motor neuron: a case report in a stroke patient.

OBJECTIVE: To study the effect of the cutaneous silent period (CSP) on spontaneous muscle activity occurring after an upper motor injury from stroke, with a goal of developing an insight into the origin of the pathological activity.
METHODS: A patient with an acute right centrum semiovale ischemic stroke had left hemiparesis. Fibrillation potentials and positive sharp waves were recorded in several left arm muscles. CSP silent period studies were performed in both arms.
RESULTS: The CSP inhibited the volitional activity in the unaffected right arm. In the plegic left arm, fibrillation potentials and positive sharp waves persisted during the time period during which the CSP would have been expected, based upon the right-sided studies.
CONCLUSIONS: Spontaneous activity after a cerebrovascular accident was resistant to inhibition from CSP. These findings suggest that the localization of the origin of the spontaneous activity is distal to the upper motor neuron. A confirmatory study with more patients and in a variety of stroke subtypes would strengthen this conclusion.