Skeletal muscle findings in experimental autoimmune encephalomyelitis

Skeletal muscle is a target organ in multiple sclerosis, a chronic debilitating disease of the central nervous system caused by demyelination and axonal deterioration. Since the experimental autoimmune encephalomyelitis model reproduces the relapsing-remitting course found in most multiple sclerosis patients, this model was used to compare the histological features of skeletal muscle at onset with those observed at the start of the second relapse.

Histological, histochemical and ultrastructural changes, as well as biochemical oxidative damage and antioxidant-system markers, were examined in the soleus and extensor digitorum longus muscles of Dark Agouti rats in which experimental autoimmune encephalomyelitis had been induced by active immunization using myelin oligodendrocyte glycoprotein.

Histological examination at disease onset revealed ragged-red fibers and ultrastructural evidence of mitochondrial degeneration. At the second relapse, neurogenic changes included a wide range of cytoarchitectural lesions, skeletal muscle atrophy and the appearance of intermediate fibers; however, differences were observed between soleus and extensor digitorum longus lesions. Biochemical tests disclosed an increase in oxidative stress markers at onset, which was more pronounced at the second relapse.

Microscopic findings suggest that two patterns can be distinguished at disease onset: an initial phase characterized by muscle mitochondrial alterations, and a second phase dominated by a histological muscle pattern of clearly neurogenic origin.