Toxic and neurogenic factors in chloroquine myopathy fibre selectivity.

Biopsies from soleus and extensor digitorum longus (EDL) muscles obtained in rats with an experimental chloroquine myopathy were studied ultrastructurally. Two different histopathological pictures were observed: type I fibres from soleus exhibited a vacuolar myopathy with an almost normal sarcomeric structure; type II fibres from EDL did not show vacuoles but changes similar to neurogenic atrophy. Our results suggest that chloroquine produces direct toxic effects in type I fibres and secondary neurogenic damage in type II fibres.