Dystrophy-like myopathy in a foal.

Two muscle biopsies from the gluteus medius and semitendinosus muscles of a six-month-old male standardbred trotter with clinical signs of hypertrophy and hypertonicity, and an electromyogram showing myotonic discharges in the glutei, semitendinosus and semimembranosus muscles, were examined by histological, histochemical and ultrastructural methods. Histologically, the main findings were variations in fibre size and shape, vacuolisation, hyalinisation and the splitting of fibres, an increase in the numbers of internal nuclei, infiltration by connective tissue and fat, hypertrophy and the predominance of type I fibres, and clusters of one type of fibre. These histological results resembled those in human muscular dystrophy.