Morphologic changes in the muscles of patients with postpoliomyelitis neuromuscular symptoms.

Thirty-five muscle biopsies were performed on 27 patients with postpoliomyelitis progressive muscular atrophy (PPMA) (8 patients had two biopsies) and 5 asymptomatic postpolio patients in an attempt to define diagnostic criteria for the newly weakening muscles and to provide insights into the mechanism of the disease. PPMA muscles that had been left weak since the original illness showed a mixture of myopathy with new and old denervation including group atrophy and nuclear clumps. Fully recovered or originally spared PPMA muscles showed signs of reinnervation and recent denervation. Perivascular or interstitial inflammatory cells (predominantly lymphocytes unrelated to phagocytosis) were noted in 40% of all the PPMA biopsies. It is concluded that (1) postpolio muscle biopsies show a spectrum of morphologic changes that depend on whether the biopsied muscle was originally affected and had fully or partially recovered, (2) the newly weakened muscles show signs of recent denervation, and (3) the presence of reinnervation in the asymptomatic muscles and the patterns of recent and old denervation in PPMA muscles provide information regarding the degree of compensation of the surviving motor neurons and their apparent failure for further reinnervation via axonal sprouting.