Postpolio muscular atrophy. Diagnostic utility of macroelectromyography
D. J. Lange, T. Smith and R. E. Lovelace
Department of Neurology, Columbia-Presbyterian Medical Center, New York, NY 10032.
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 microV; normal level, less
than 390 microV). Muscles with new weakness and atrophy had smaller than
expected macro-EMG amplitude (130 to 450 microV). Two muscles with weakness
and atrophy unchanged since the original childhood infection had markedly
increased macro-EMG amplitude (1710 and 1860 microV), 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.