Experimental corticosteroid myopathy.

The steroids triamcinolone, dexamethasone, beta-methasone, and cortisone were administered i.p. to adult rats for 14-63 days. The extensor digitorum longus (EDL, white muscle) and soleus (SOL, red muscle) muscles were examined histologically and histochemically. Triamcinolone was the most potent lesion-producing drug. Selective involvement of muscles, and of the fiber types within them was observed: Necrotic changes were seen only in the type 1 fibers of the SOL; atrophic fibers were observed in the type 2 fibers of both the SOL and the EDL.