Electrophysiologic findings in amyloid myopathy

Myopathy is an uncommon manifestation of systemic amyloidosis. A retrospect ive chart review of 17 patients seen between 1975 and 1997 with biopsy-prov en amyloid myopathy was performed to characterize the electrophysiologic fe atures. Nerve conduction study abnormalities occurred in 14 of 17 patients (82%). The most common abnormality was a low peroneal and/or tibial compoun d muscle action potential amplitude (n = 9). Mild abnormalities also occurr ed in seven other nerves. Repetitive stimulation at 2 Hz in 10 nerves was n ormal, Electromyography demonstrated fibrillation potentials in 69% of musc les, most frequently in the gluteus medius (90%) and paraspinals (87%), The fibrillation potentials were sparse in 60%. Short-duration, low-amplitude motor unit potentials (MUPs) were found in 72% of the muscles examined, wer e mild in 81%, and were more common in proximal muscles. Long-duration MUPs were found in 19% of muscles and a mixed population of MUPs in 4%, These f indings are similar to those of common chronic, inflammatory myopathies. (C ) 1999 John Wiley & Sons, Inc.