Electromyographic Study of Thoracic Paraspinal and Rectus Abdominis Muscles in Amyotrophic Lateral Sclerosis.

Purpose: The aim of our study was the comparison of active denervation (fibrillation and/or positive sharp wave potentials) in thoracic paraspinal muscles with rectus abdominis in patients with definite amyotrophic lateral sclerosis.
Methods: Ninety-five consecutive patients with clinically definite amyotrophic lateral sclerosis according to the revised El Escorial criteria were studied prospectively over a 5-year period. Concentric needle electromyogram was performed in thoracic paraspinal muscles, in the rectus abdominis at the T9 level, and in limb muscles.
Results: Active denervation was present in thoracic paraspinal muscles in 75 patients (79%) and in rectus abdominis in 62 patients (65.3%) (P = 0.02). No significant difference was found between the two muscles regarding the type of onset (bulbar, upper, and lower limbs), amyotrophic lateral sclerosis functional rating scale values, and creatine phosphokinase levels.
Conclusions: Thoracic paraspinal muscles are the first to be tested in patients with amyotrophic lateral sclerosis. Absence of active denervation in T-PSM is rarely associated with active denervation in rectus abdominis.