Observations on the Short-Term Effects of Chloroquine on Skeletal Muscle An Experimental Study in the Rabbit

Abstract A study of the short-term effects of chloroquine on skeletal muscle in rabbits is reported. Minimal but significant changes consistent with the development of a myopathy were found in serum enzymes (CK and LDH) and in the electromyogram in the treated animals. These animals also showed a “myasthenic” response to tetanic stimulation of limb muscles which did not appear to be related merely to the presence of the drug in the circulation. No histological evidence of a vacuolar myopathy was found in any of the animals but all the treated animals showed foci of necrosis and phagocytosis in skeletal and cardiac muscle. Histochemical studies showed abnormal localization of SDH in cardiac muscle and electron-microscopy showed many apparently abnormal mitochondria in both cardiac and skeletal muscle. Other electron-microscopic changes found in skeletal muscle included Z-band and neighbouring filament degeneration and dilatation of the longitudinal reticulum. The possible significance of the changes is discussed with particular reference to the pathogenesis of chloroquine myopathy.