Plasma cell pododermatitis
Plasma cell pododermatitis ('Spongy pad') is a rare inflammatory skin disease of cats.
There appears to be no breed, age or sex predilection for this diseases. A number of incriminating causes have been implicated, of which FIV, Mycobacterium spp and FHV have been mentioned, as well as Anatrichosoma spp nematode infection.
Seasonal occurrence has been suggested but not confirmed. An immune-mediated relationship has been hypothesized since hypergammaglobulinaemia appears to be a consistent finding. Additional features such as glomerulonephritis, leucoclastic vasculitis and plasma cell stomatitis may also occur.
The disease usually starts with marked pain in one or more metacarpal or metatarsal footpads. These swollen footpads are soft and painful in the center, causing lameness. With time, swellings, which ulcerate and bleed at the slightest touch, develop on one or more metacarpal or metatarsal footpads and/or digits. The lesions often look purple and crosshatched with pale striae and feel spongy. The older the lesions are, the more likely they are to develop secondary infection. Cats are sometimes affected systemically with pyrexia, listlessness, anorexia, anemia and peripheral lymphadenopathy. In a minority of cases, there may be concurrent plasma cell stomatitis, immune-mediated glomerulonephritis or renal amyloidosis.
Histopathologically, there are dense infiltrates of plasma cells with smaller numbers of lymphocytes and macrophages. Mycobacteria have also been reported in a small number of cases, but is not the norm. That there is a variable histopathological appearance to pododermatitis in cats, suggests that the clinical signs may well be the result of any number of etiological agents, with infections (bacteria and viruses) and hypersensitivity as possible primary factors.
The disease should be differentiated from feline lung digit syndrome.
Spontaneous recovery is common in some cases after 2-3 months, and this appears to reflect the multiple etiology. A few cases have been treated surgically, but the majority are treated with immunomodulatory drugs such as Interferon-Ω.
Azithromycin and Doxycycline appear to have some success in 35-50% of cases. Recovery reflects the ability to determine the causative agent and/or treat with appropriate antimicrobial/immunomodulatory medication.
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