Selected topics in feline dermatology (Proceedings)

Pemphigus foliaceous (PF)

PF is the most common immune-mediated skin disease of the cat. It often begins on the face and pinnae, but also usually involves the foot pads and claw beds. Crusts and pustules on the face and pinnae, hyperkeratotic footpads, a purulent to caseous discharge with crusting around the nail beds, and crusting of the nipples are all common findings.

The diagnosis is made through skin biopsy and cytology. Treatment involves immunosuppressive medications such as corticosteroids, chlorambucil, cyclosporine, chrysotherapy (gold salts), and other medications. The goal of treatment is to obtain remission with more potent medications and dosing regimens, and then slowly transition to safer, preferably non-steroid based, maintenance protocols.

Feline plasma cell dermatitis

This is a condition of unknown pathogenesis, yet is thought to be immune mediated. Plasma cells infiltrate the foot pads causing very large swellings primarily of the metacarpal and metatarsal pads. There is usually more than one foot pad affected and the swelling is usually painless. In one study, 50% of cats affected had concurrent FIV infection. The diagnosis can often be made by physical examination alone. Fine needle aspiration can be supportive, and skin biopsy confirmative. Corticosteroids at immunosuppressive doses are effective in most cases followed by a slow taper. Doxycyline has also shown to be beneficial although response time is slow. In difficult cases, chrysotherapy or surgical excision of the fatty pad may be necessary.

Cutaneous xanthomas

These are rare granulomatous lesions associated with hyperlipidemia or diabetes mellitus. Xanthomas typically appear as pale yellow to white papules, nodules, or plaques with surrounding erythema. These are often found over bony prominences, or on the trunk, head, or distal extremities. Histological examination reveals foamy macrophages and multinucleate histiocytic giant cells within the dermis. These foamy macrophages can also be seen in impression smears from the lesions or from fine needle aspirates of larger papules or nodules. Chemistry profiles that include cholesterol and triglycerides, as well as screening for diabetes mellitus should be performed. Controlling the diabetes, if present, as well as feeding a low fat prescription diet results in resolution within 30 days in most cases.

Bowen's disease/squamous cell carcinoma in situ

This is a rare disease of older cats that is thought to be a malignant transformation of viral papillomas causing carcinoma in situ lesions. These are characterized by hyperkeratotic, often pigmented macules and plaques that are most often seen on the head, neck, dorsal thorax, ventrum, and legs. When these lesions are initially discovered, it is a good idea to shave the cat in that region, as early, mild lesions can easily be missed otherwise. The more chronic lesions may be verrucous, have keratin horns protruding from the skin, or may be ulcerated. In one study, 27% of cats had developed invasive squamous cell carcinoma in focal areas. The diagnosis is established through skin biopsies. Carbon dioxide laser ablation of the lesions is very effective in the areas that are still "in situ" since the diseased skin is confined to the epidermis. Topical 5 % imiquimod has been effective in many cases, and the use of oral retinoids has been mentioned in the literature.

Bronchiogenic carcinoma with distant digital metastasis

Older cats with asymptomatic bronchiogenic or squamous cell carcinoma of the lung may develop destructive lesions on the digits due to metastasis. Usually, there are multiple digits involved and usually on different feet. Distant metastasis can also be found on the head, belly, lip, leg, or lumbar area.

Paraneoplastic syndromes

There are two rare syndromes in the cat: an exfoliative dermatitis associated with thymomas, and paraneoplastic alopecia in cats with pancreatic or bile-duct carcinomas. The clinical signs, diagnosis, and treatment will be discussed.