Cutaneous histiocytosis in dogs

Multifocal cutaneous histiocytic lesions were recognized in 9 dogs. Clinically, the dogs had multiple erythematous plaques or nodules in the skin (1 to 5 cm diameter). Histologically, the lesions were comprised of dermal or pannicular infiltrates of large histiocytic cells, with varying numbers of other inflammatory cells intermixed. By electron microscopy, the cells resembled those of canine cutaneous histiocytoma. The lesions seemed to wax and wane and appeared in new sites, regardless of treatment. The dogs ranged in age from 2 to 13 years; 7 dogs were under 6 years of age. Both sexes and various breeds were represented. An infectious agent could not be identified.