Soleus-specific myopathy induced by passive stretching under local tetanus.

Twenty-four adult albino rats were injected with tetanus toxin into the right gastrocnemius muscle and then subjected to sustained dorsiflexion of the right ankle joint for 2 to 14 days. Histologic examinations of the soleus after this procedure showed myopathic changes, characterized by variations in fiber diameters, myonecrosis with opaque fibers, interstitial fibrosis, and small groups of regenerated fibers. Electron microscopy revealed derangement of T-tubules immediately adjacent to the sarcolemma in the early degenerative stage. The size and wet weight of soleus increased compared to that of the control side between 2 and 5 days post-tetanus. Serum GOT, LDH, and creatine kinase (CK) levels were elevated especially in the early degenerative stages. Peri- and endomysial fibrosis developed gradually from about 3 days post-tetanus. Pathomechanisms inducing these changes were discussed.