Denervation atrophy in three horses with fibrotic myopathy.

Three horses with fibrotic myopathy were examined for neuromuscular disease. In 2 horses, concentric needle electromyography was performed. Dense spontaneous activity suggestive of denervation, was found in multiple thigh muscles of 1 of the 2 horses. All 3 horses were euthanatized. Histochemical and histologic examination of tissue specimens was performed. All horses had degenerative lesions in peripheral and intramuscular nerves. Angular atrophy of type-1 and type-2 muscle fibers, indicative of denervation atrophy, was seen in multiple muscle specimens from all 3 horses. One horse was found to have a fracture of the greater trochanter, with fibrous entrapment of the sciatic nerve at that site. The cause of the peripheral neuropathy was not determined in the other 2 horses. It was concluded that peripheral neuropathy should be considered in horses with fibrotic myopathy.