Feline plasma cell pododermatitis is an uncommon disease of cats characterized by swelling in multiple footpads. Lameness and ulceration are common secondary complications. The cause of the disorder is unknown. Lesions often respond to glucocorticoids and other immunosuppressive drugs; however, an infectious cause is also possible. Several recent studies have reported a partial or complete response to doxycycline; this response could be due to the drug's antiinflammatory effects or because the patient has a doxycycline-responsive infection. In this study, tissue specimens from 14 cats with plasma cell pododermatitis were stained with a polyclonal anti-Mycobacterium bovis antibody cross-reactive to several bacterial and fungal pathogens, including Toxoplasma gondii, Chlamydophila felis, Ehrlichia canis, Mycoplasma species, Bartonella henselae, feline herpesvirus, and Anaplasma phagocytophilum. The results of polymerase chain reaction (PCR) testing of all 14 footpad samples were negative for these pathogens. This study failed to demonstrate the presence of infectious agents via immunohistochemical and PCR testing in cats with plasma cell pododermatitis.

COMMENTARY: Biopsy is necessary for a definitive diagnosis of plasma cell pododermatitis. If possible, select a non-weight-bearing pad and avoid necrotic or ulcerated areas. Lesions may wax and wane; however, in my experience cats with waxing and waning lesions are least likely to be presented to the veterinarian. They tend to develop discoloration and "puffy footpads," and by the time the owner is concerned enough to make an appointment, the lesions have resolved. Lesions that are extremely painful or widespread are best treated initially with aggressive glucocorticoid therapy (4 mg/kg PO once daily until resolution). Less painful lesions often respond to doxycycline (5-10 mg/kg PO Q 12 H). A response may take 30 to 60 days, and drugs should not be tapered until the lesions resolve. Some cats require lifelong therapy. Cyclosporine (5 mg/kg PO Q 24 H) is a recent addition to treatment protocols. Very large ulcerated or pedunculated lesions may need surgical excision.

An immunohistochemical and polymerase chain reaction evaluation of feline plasmacytic pododermatitis. Bettenay SV, Lappin MR, Mueller RS. Vet Pathol 44:80-83, 2007.