Systemic amyloidosis in a mare.

A mare with chronic cachexia had multiple skin nodules, abdominal masses (attached and free floating), and large lymph nodes. Fine-needle aspiration cytologic evaluation of a skin mass revealed multinucleated giant cells surrounding eosinophilic material. Histologic evaluation revealed extensive amyloid deposits within the masses, lymph nodes, and the interstitium of many organs. The presence of systemic (visceral) and organ-limited (cutaneous) forms of amyloid is rare in horses. Amyloid congophilia was retained after potassium permanganate oxidation. The fibrils were thus distinct from the AA (secondary) fibrils that are found in most cases of equine amyloidosis, suggesting that this mare may have had primary amyloidosis. Regardless of fibril type, the presence of multinucleated giant cells in association with eosinophilic material in cytologic preparations of skin nodules may suggest a differential diagnosis of amyloidosis in horses.