PLASMA CELL PODODERMATITIS
(sometimes called "PILLOW FOOT")
Plasma cell pododermatitis is a foot pad disease of cats. It is fairly classical in its appearance yet its significance is poorly understood. "Plasma Cell Pododermatitis" literally means foot inflammation involving infiltration by "plasma cells." Plasma cells are activated lymphocytes in full maturity, enthusiastically producing antibodies in response to some kind of inflammatory process, usually but not necessarily infection.
The fact that an activated immunological cell is involved implies that there is some sort of immune stimulation in the genesis of this disease. Supporting this idea is the observation that therapy targeting the immune system generally controls the disease. So it looks like there is an immunological basis for this disease but, unfortunately, understanding has not progressed far enough to suggest an actual cause for the immunologic problem. That said, understanding of plasma cell pododermatitis has not progressed far enough to begin to suggest the specific nature of any such immune-mediated cause. Some studies have found a link between plasma cell pododermatitis and Feline Immunodeficiency Virus infection so it is very important to screen an affected cat for this virus. Exactly what the link is between these two conditions remains unclear but approximately 50% of cats with plasma cell pododermatitis are FIV+. Other cats will respond to a food allergy diet trial which suggests allergy may be involved in some cases. It may well be that many factors can be involved in creating this disease.
(original graphic by marvistavet.com)
CONFIRMING THE DIAGNOSIS
An affected foot pad develops a classic "mushy" appearance and balloons out as shown in the picture above. The skin of the pad may develop a purplish tint and may even ulcerate. All four feet may or may not be affected but rarely is only one foot afflicted. Any age, gender or breed of cat can be affected. Many cats are not painful and require no treatment but some cats will be lame on their most severely affected foot. The point is that there is variability in how cats demonstrate their disease. On blood tests, cats with plasma cell pododermatitis usually have elevated numbers of circulating lymphocytes and high circulating antibody (globulin) levels so such findings are supportive of making this diagnosis. Further, other foot pad swellings such as tumors, insect bites, or proliferations from Eosinophilic Granuloma Complex usually only affect a single foot. If the physical appearance of the foot is not classic for plasma cell pododermatitis, a needle aspirate or even biopsy of the foot pad should confirm the presence of plasma cells thus leaving no question.
Modification of the underlying immune reaction is the core of therapy for cats in which therapy is deemed necessary. At this time, the treatment of choice is oral doxycycline. While doxycycline is an antibiotic, it also has immunomodulating properties and we believe it is these properties that are working in the treatment of plasma cell pododermatitis. Approximately 50% of affected cats will show a good response after two months of therapy. When the condition is in adequate remission, the doxycycline is continued for several months further before discontinuing and seeing if the condition recurs.
Alternatively, high doses of an oral steroid such as prednisone may be helpful for cats that did not respond to doxycycline. Cyclosporine, another immunomodulator which is available as a liquid, has also received attention for treating this condition. Large ulcerated masses on the footpads may require surgical removal. In most cases, the condition is manageable and the cat can be made comfortable.
Page last updated: 1/21/2023