Feline Progressive Histiocytosis: A Crappy Cat Disease

This is a really interesting (albeit sad) case that was shared by Dr. Lindsey Citron earlier this year (thank you for sharing, Lindsey!). 

This is a 12 y/o MC DSH cat that had a long history of swollen digits on all four feet, erythematous, ulcerative, and purulent pododermatitis. They ended up FNA’ing an alopecic, raised, plaque like lesion on the dorsum.

The cytology shows a weird population of round cells with histiocytic-like features (moderate amount of lightly basophilic cytoplasm, rounded nuclei, stippled chromatin). Histopath and immunohistochemistry (CD18+) went on to confirm this as a case of feline progressive histiocytosis.

FPH is a crappy disease. These cells are derived from interstitial dendritic cells (remember we talked about those last week?). Cats get these variably sized nodules, often on their face/head and extremities, which can wax and wane but don’t regress on their own. It’s considered to be a kind of low-grade histiocytic sarcoma, and lesions can sometimes spread from the skin into organs and lymph nodes.

Even though I don’t dabble in treatment, according to my reading, they don’t respond well (or for long) to immunosuppressive therapies.

Have any of you seen a case of this in practice? It’s not a common disease, but an important one!