Sterile Pyogranulomatous Dermatitis and Panniculitis.

Canine sterile pyogranulomatous dermatitis and panniculitis is an infrequently described syndrome. No autoantigen, or exogenous antigen, inflammatory stimulus has been identified. This syndrome is characterized by pyogranulomatous nodules, plaques, and ulcers of variable extent and severity. Prodromal and concurrent nonspecific clinical and hematologic signs of inflammation may occur. This waxing and waning condition is typically responsive to systemic immunomodulation. Lifelong therapy may be required to prevent relapse. Differential diagnoses include bacterial and fungal nodular dermatoses, neoplasia, and cutaneous reactive histiocytosis. Diagnosis is achieved via diagnostic exclusion of infectious causes and supportive histopathology findings.