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Diagnostic Utility of Macroelectromyography

Dale J. Lange, MD; Torben Smith, MD; Robert E. Lovelace, MD

Arch Neurol. 1989;46(5):502-506.

Abstract
• Muscles recovered from previous poliomyelitis may exhibit new weakness and wasting years after the original infection (postpolio muscular atrophy). Routine electrophysiological and morphological techniques may not differentiate weakening muscles from previously affected but stable muscles. We used quantitative motor unit potential analysis, single-fiber electromyography, and macroelectromyography (macro-EMG) to determine if these techniques could identify weakening muscles. We classified 18 previously affected muscles according to strength from 12 patients who had had poliomyelitis 18 to 50 years earlier. Muscles of normal strength had large-amplitude macro-EMG signals (1000 to 4110 µV; normal level, <390 µV). Muscles with new weakness and atrophy had smaller than expected macro-EMG amplitude (130 to 450 µV). Two muscles with weakness and atrophy unchanged since the original childhood infection had markedly increased macro-EMG amplitude (1710 and 1860 µV), suggesting the increased macro-EMG amplitude is due to stable reinnervation not strength. Mean motor unit potential duration and amplitude were lower in newly weakened muscles, but jitter, fiber density, and blocking were similar in all muscles regardless of strength. We conclude that low-amplitude macro-EMG signals may be useful in the identification of muscles weakened by postpolio muscular atrophy.

Author Affiliations
From the Department of Neurology, Clinical Neurophysiology Laboratories, Columbia-Presbyterian Medical Center, New York. Dr Smith is now with the Laboratory of Clinical Neurophysiology, Rigshospitalet, Copenhagen.

Footnotes
Accepted for publication Nov 3, 1988.

Reprint requests to Neurological Institute, Columbia-Presbyterian Medical Center, 710 W 168th St, New York, NY 10032 (Dr Lange).

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