The Relationship Between Spontaneous Activity and Integrity of the Lower Motor Neuron
By Dr. Cassie Renfro
Objective:
To determine if the presence of spontaneous activity in muscles with grade zero motor scores represents complete muscle denervation.
Design/Methods:
Prospective study in which 13 subjects with traumatic cervical SCI were studied at a mean of 31.4 days following injury. An upper extremity ISNCSCI evaluation was completed on all subjects. A needle EMG and an electrically stimulated manual muscle test (SMMT) was completed on all upper extremity muscles with a grade zero motor score.
Results:
The motor scores of 125 key upper extremity muscles were assessed in thirteen individuals. Fifty-five key muscles were identified with a motor score of zero. The needle EMG identified spontaneous activity (fibrillation potentials/positive sharp waves) in 42/55 of the muscles studied. In these muscles, a SMMT score of zero was obtained in 10.9% (6/55), one to two in 45.5% (25/55), and > three in 43.6% (24/55). At an average of 1-month after SCI, 87.5% of the muscles tested that showed a strong response to the SMMT (grade ≥ 3) had EMG evidence of denervation. By contrast, 50% of the muscles that appeared to be fully denervated, based on the response of the SMMT (grade “0”) had EMG evidence of denervation.