What is plasma cell pododermatitis?
Also known as pillow foot, feline plasma cell pododermatitis (FPP) is a rare autoimmune disorder characterised by inflammation of the paw due to infiltration of plasma cells (a type of white blood cell known as a plasmacyte that secretes antibodies in response to infection).
One pathologist searched the database of an unnamed diagnostic laboratory which found a higher incidence in male cats, with a median age of 6 years and an age range of 9 months to 17 years.
The etiology of plasma cell pododermatitis is unknown but it is thought immune hyperactivity is the root cause, one study found more than 50% of affected cats were positive for feline immunodeficiency virus or feline leukemia virus. Other possible triggers include food hypersensitivity, glomerulonephritis and plasmacytic stomatitis.
Symptoms can vary from cat to cat depending on the severity of the condition. Lesions may be confined to a single but typically affects multiple pads. Any footpad can be affected, but FPP is seen most often on the large metacarpal pads on the front legs or the metatarsal pads on the hind legs.
- Purple, spongy swelling on one or more of the paw pads followed by hyperkeratosis and ulceration which may bleed
- Secondary bacterial infection of the ulcerated lesion
- Erythema (redness) or purple cast closely resembling bruising
- Splitting of the footpad
- Excessive paw licking
The veterinarian will perform a physical examination and obtain a medical history from you including underlying health issues and when did clinical signs first develop. A tentative diagnosis may be made based on the gross appearance of FPP lesions. However, a diagnostic workup will be necessary to evaluate the overall health of the cat and rule out other possible causes such as tumours, eosinophilic granuloma complex, pemphigus, vasculitis, and acetaminophen toxicosis.
Baseline tests: Biochemical profile, complete blood count and urinalysis can provide information on the overall health of the cat as well as check for underlying infections. A complete blood count may reveal elevated lymphocytes and hypergammaglobulinemia.
FIV test: This blood test looks for antibodies to the feline immunodeficiency virus.
Biopsy and histopathology: A diagnosis is made by obtaining a biopsy from the affected pad and histopathology, which is the microscopic examination of the sample. This will reveal infiltration of plasma cells along with a smaller number of macrophages and lymphocytes.
The goal of treatment is to address the underlying cause if one can be established as well as address the pododermatitis. Some cats with mild plasma cell pododermatitis may spontaneously recover.
There are several treatment options available which can vary depending on the severity of the condition.
Antibiotics: Doxycycline is an antibiotic with immunomodulating effects which help to suppress the immune system. 50% of cats showed a good response after two months of therapy. Cats will remain on doxycycline for several months before treatment is discontinued. Doxycycline has the potential to cause inflammation of the esophagus (esophagitis), therefore it is recommended that a pill pocket or gel capsule be used to administer the drug followed by some water to wash it down.
Immunosuppressive therapy: Cats who don’t respond to doxycycline can benefit from oral steroids such as prednisolone or cyclosporine to suppress the immune system.
Methylprednisolone acetate (Depo-Medrol) is a slow-release, long-acting injectable drug which avoids the need to medicate the cat daily, however, there are potential side effects with this medication and it is contraindicated in cats with diabetes, chronic kidney disease, congestive heart failure and Cushing’s syndrome.
Dexamethasone is a shorter-acting steroid that may be administered via injection at home.
Surgery: Large and ulcerated masses on the foot which don’t respond to medical therapies may require surgical excision.
The prognosis for cats with plasma cell pododermatitis is good. Cats who have achieved remission may be weaned off medication after several months. Some cats will require lifelong therapy.