Differential analyses of EMG findings in motor neuron lesions.

The principle in electromyography that positive sharp waves (PSW) and fibrillation potentials (FP) are pathognomonic of lower motor neuron (LMN) pathology is challenged by recent reports that the same potentials are observed in upper motor neuron (UMN) lesions. We have also observed positive sharp waves and fibrillation potentials in patients with UMN lesions, without conditions that involve the LMN. This study was undertaken to ascertain if there are differences in the potentials between the LMN and UMN lesions. Twenty-five UMN and 25 LMN patients were electromyographed. Manual and computer analyses were used to compare parameters from positive sharp wave and fibrillation potentials. Our findings indicate that there are interlesion differences in the mean frequency of occurrence ratio of PSW to FP and in some of the durational wave parameters.