A pillow foot. Photo by MarVistaVet

Plasma cell pododermatitis is a foot pad disease of cats that 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 suddenly and severely producing antibodies, usually in response to an infection or at least in response to some kind of inflammatory process.

The fact that a cell of the activated immune system is involved implies that there is some sort of immune stimulation in the genesis of the 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. Some studies have found a link between plasma cell pododermatitis and feline immunodeficiency virus (FIV) infection so it is important to screen an affected cat for this virus. Exactly what the link is between these two conditions remains unclear but approximately 50 percent of cats with plasma cell pododermatitis are FIV-positive. Other cats will respond to a food allergy diet trial, which suggests that allergies may be involved in some cases. It may well be that many factors can be involved in creating this disease. 

Confirming the Diagnosis

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. Some pads may ulcerate while others do not. The point is that there is variability in how cats demonstrate their disease. 

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. In contrast, other swollen pad conditions such as tumors, insect bites, and eosinophilic granculoma usually only involve one foot only. In short, puffy pads on multiple feet, makes plasma cell pododermatitis and very likely diagnosis. On blood tests, cats with plasma cell pododermatitis usually have elevated numbers of circulating lymphocytes, low numbers of platelets (blood clotting cells), and high circulating antibody (globulin) levels so such findings are supportive of making this diagnosis. 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.

 A needle aspirate can be used less invasively to harvest some cells from the affected foot and check for an abundance of plasma cells.

Treatment

Modification of the underlying immune reaction is the core of therapy for cats in which therapy is deemed necessary by your veterinarian. 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 effective in treating plasma cell pododermatitis. Approximately 50 percent of affected cats will show a good response after two months of therapy. When the condition is in adequate remission, the doxycycline may be discontinued though if the condition recurs, medication must re-start. Alternatively, high doses of an oral steroid such as prednisolone may be helpful for cats that did not respond to doxycycline. Cyclosporine, another immunomodulator that is available as a liquid, has also received attention for treating this condition. Should medicating a cat daily prove a bit daunting, another therapy choice might involve injections of methylprednisolone acetate (depomedrol), a long-acting steroid, though there is some potential for side effects. Alternatively, injections of dexamethasone, a shorter-acting steroid, can be given regularly at home.

Large ulcerated masses on the footpads may require surgical removal. In most cases, the condition is manageable and the cat can be made comfortable.