Electromyographic and morphological functional compensation in late poliomyelitis.

Patients with prior poliomyelitis may experience muscle function deterioration decades after onset of disease. The present study is aimed at describing electromyographic and morphometric evidence of muscular compensation and of on-going muscular instability. Ten subjects 42-62 years of age with onset of polio 25-52 years earlier were studied with macro EMG, single-fiber EMG (SFEMG), muscle strength measurement, and morphometrical analysis of muscle biopsies from the vastus lateralis muscle. SFEMG revealed increased fiber density (FD) and large macro-MUP potentials indicating pronounced reinnervation as compensation to loss of motor neurons. From electrophysiological data of motor unit size, morphometric measures of fiber size, and muscle strength data, the minimal degree of motor neuron loss was estimated to be greater than 70%.