Electromyographic and morphological functional compensation in late poliomyelitis

Abstract

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%.

An 8-year longitudinal study of muscle strength, muscle fiber size, and dynamic electromyogram in individuals with late polio

“…33 Differences in patient material and electrophysiological techniques may explain existing discrepancies. As shown in our previous reports 11,26 from the same group of polio subjects as in this study, reinnervation causes large motor units, sometimes very large. They increase in size with time in most cases, which has been attributed to an ongoing denervation-reinnervation process.…”

“…Subjects acknowledging new weakness, had also lost significantly more strength than other individuals. As already demonstrated in our initial studies, 11,14 the polio-affected muscles were characterized in macro EMG by large motor units, with an 11-fold amplitude increase compared with age-matched control values. The muscle fiber areas were large, on average close to twice control values.…”

Disability in a 4-year follow-up study of people with post-polio syndrome

“…Prior longitudinal studies have assessed muscle strength in one leg as "the worst"; however, the muscle strength in those studies was in general higher than in the present group of individuals, which could be a factor explaining the different findings. It is not known whether the lack of demonstrated reduction in muscle strength in our study corresponds to stable compensatory mechanisms (re-innervation and muscle fibre hypertrophy) (25). This can also be caused by altered relative contribution of these mechanisms or reflect that a deterioration in function could be influenced and/or delayed by a change in lifestyle with less physical activity.…”

Quantitative EMG analysis and longitudinal nerve conduction studies in a Refsum's disease patient

“…These findings indicate pronounced reinnervation as compensation for the loss of motor units, as has been shown by Einarssen et al 4 who demonstrated that in late poliomyelitis concomitant macro-EMG study with muscle strength measurements and morphometrical analysis muscle biopsies allows estimation of the extent of axonal loss even though the interpretation may be complicated by fiber atrophy o r hypertrophy. I n their study, when macro-MUP mean amplitude was about 6, the percentage of remaining motoneurons was about 30%, and when the amplitude was about 15 the percentage was about 20%.…”