Crusty cats: feline pemphigus foliaceus.

Pemphigus foliaceus (PF) is an immune-mediated disease that causes pustules and crusted lesions, most commonly on the pinnae, nasal planum, periocular area, chin, and feet of affected cats. Acantholytic cells caused by degradation of intercellular adhesions are often seen on cytology but are not pathognomonic for PF. A definitive diagnosis is made based on histopathology showing subcorneal pustules with nondegenerate neutrophils and acantholytic cells. PF is treated with immunosuppressive doses of corticosteroids alone or in combination with other immunosuppressive medications, such as chlorambucil or cyclosporine. Most patients require lifelong treatment with these medications to keep the disease in remission.