Needle electromyography of the rectus abdominis in patients with amyotrophic lateral sclerosis.

We examined the role of needle electromyography (EMG) of the rectus abdominis (RA) in assessing thoracic involvement in amyotrophic lateral sclerosis (ALS). Needle EMG of the RA was performed in 67 patients with sporadic ALS and 110 healthy controls. The presence of abnormal spontaneous activity, configuration of motor unit action potentials (MUAPs), and recruitment pattern of motor unit potentials were examined. In ALS patients, MUAPs in the RA were of prolonged duration, large amplitude, and showed increased prevalence of polyphasic waveforms compared to controls. Significant differences in MUAP parameters, presence of abnormal spontaneous potentials, and interference patterns were noted between ALS patients and controls. Additionally, we found that active denervation was more frequent in the RA of ALS patients with dyspnea than those without dyspnea. Thus, conventional needle EMG of the RA is a valuable electrophysiological method to assess clinical and subclinical involvement of thoracic lower motor neurons in patients with suspected ALS.