Plasma cell pododermatitis (PPD) is a rare disorder of the foot pads of cats. Colloquially it is often called “pillow foot!” While this may sound cute, the disease itself can be quite painful for affected animals! The etiology of the disease is unknown, but it is thought that immune stimulation may play a role in the development of this disease. There is an association with feline immunodeficiency virus, with about 50% of cats with PPD being positive for FIV.
PPD is characterized by infiltration of plasma cells into the tissue of the paw pad. This cellular infiltration results in pronounced swelling of the foot pads, and can produce soft, mushy paw pads (hence the name pillow paws). The central pads are typically affected, although the digital pads can be involved. Normally, multiple foot pads are affected. Ulceration is a common finding. The pads can be quite painful for the cat to walk on, and many cats will present with an initial complaint of lameness! Although this condition is almost always limited to the foot pads, cases with nasal swelling with plasma cell infiltrates and cases with plasma cell stomatitis have been described.
As you can see from the images, the clinical appearance is quite striking! The primary differential diagnosis is an eosinophilic granuloma, although this is usually limited to one foot pad. Aspiration cytology of PPD should reveal predominantly plasma cells. Although definitive diagnosis is classically achieved via biopsy, it may not be necessary in a cat with swelling of multiple foot pads and consistent aspiration cytology findings. If the clinical findings and aspiration cytology are equivocal, then biopsy of the foot pad is recommended. Because many cats with PPD are FIV positive, I recommend all cases be tested.
For milder cases, I recommend starting with doxycycline at 10 mg/kg once daily. Because of risk of esophageal stricture, cats should either take a liquid form of doxycycline, or the pill should be followed by a water chaser. Treatment should continue until the pads are normal, which can take several months. Once the pads are normal, doxycycline can be tapered and can often be eventually stopped, although some cats will need ongoing therapy. In more severe cases, if the animal is quite painful, I recommend also using prednisolone at 2-4 mg/kg per day with tapering following remission. Cyclosporine use is an option for animals that need ongoing medical therapy, and are not well controlled on doxycycline alone. If secondary infection is present, an additional antibiotic is often needed since doxycycline does not work well for skin infections.
If you have any dermatology questions, I am happy to answer them!