Feline leprosy: spontaneous remission in a cat.

A two-year-old, male domestic shorthair with a solitary lesion of the right forelimb was presented for fine-needle aspiration biopsy of a suspected cutaneous, neoplastic process. Neutrophils, lymphocytes, and acid-fast bacilli packed in the cytoplasm of foamy macrophages and giant cells were seen on cytological examination. Bacteriological culture of the material from the skin lesion was negative for Mycobacterium spp. Intraperitoneal injection of homogenized material from the lesion resulted in generalized mycobacteriosis in one mouse after 10 months. Based on these results, a diagnosis of feline leprosy was made. No medical or surgical therapy was performed. Nonetheless, the lesion showed progressive and complete spontaneous remission within 3.5 months from the time of diagnosis; after 14 months, the cat still is free of disease.