MUSCLE MODIFICATIONS IN PARKINSONS-DISEASE - MYOELECTRIC MANIFESTATIONS

The muscle changes occurring in Parkinson's disease (PD) may come abou t as a consequence of the modified pattern of motor unit activation an d rigidity, which are characteristic of the disease. A tendency toward s hypertrophy of type I fibers and, in some instances, atrophy of type II fibers has been observed. Fourteen patients affected by PD and 10 age-matched controls were studied in order to investigate these muscle changes. We indirectly evaluated muscle modifications by measuring mu scle fiber conduction velocity (CV) and median frequency (MDF) of the power spectrum using automatic analysis of surface EMG, The tibialis a nterior muscle was selected for the study of contractions electrically induced by 35 Hz pulse trains lasting 30 s; the myoelectric signal wa s detected using the 4-bar electrode technique described by Broman et al. (Broman, H., Bilotto, G. and De Luca, C.J. Myoelectric signal cond uction velocity and spectral parameters: influence of force acid time. J. Appl. Physiol., 1985, 58: 1428-1437). Muscle biopsy specimens were obtained in 4 PD patients by surgical excision at the site where the EMG recording electrode had been placed. The main difference observed between PD subjects and controls was the rate of change of MDF and CV during the course of stimulated contraction; patients with PD sustaine d a smaller fatigue related decrease in both parameters compared to co ntrols, According to our histological data, this result can be explain ed by a type I fiber percentage which accounts for 79% of the myofiber population on average. As expected, the CV basal values correlated di rectly with type I fiber diameter. These data suggest that non-invasiv e surface EMG techniques are useful in assessing the modifications of muscle characteristics that are observed in PD patients and for analyz ing some aspects of the peripheral fatigue in this disease.