The lesions (crusts and pustules) of this most common immune-mediated skin disease in cats generally appear initially on the face and pinnae but characteristically cause hyperkeratosis of the footpads with a purulent/casceous discharge crusting around the claw beds. Pemphigus foliaceus is diagnosed by identifying acantholytic keratocytes on cytologic examination of skin biopsy samples. Treatment involves immunosuppressive doses of corticosteroids plus or minus the use of chlorambucil, cyclosporine or gold salt injections. After remission is achieved, the goal is to slowly transition to safer, nonsteroidal maintenance protocols. This condition can mimic chin acne and has a wide range of severity, often complicating diagnosis.
Feline plasma cell dermatitis
While the pathogenesis of this condition is unknown, it is thought to be immune-mediated. Plasma cells infiltrate the footpads, resulting in large swellings. Generally, more than one pad is affected, and while affected cats may begin to chew on them, they are often nonpainful. The condition is frequently associated with concurrent feline immunodeficiency virus (FIV) infection. It can often be diagnosed by physical examination alone and can be confirmed with skin biopsy. Immunosuppressive doses of corticosteroids (slowly tapered) are warranted and effective in most cases. Treatment with doxycycline is also beneficial, but response is slow. For recalcitrant cases, gold salt injections or surgical excision of the pad may be necessary.
This is a "fat cat" disease resulting in pale-yellow or white papules, nodules or plaques with surrounding erythema. The lesions form over body prominences and on the trunk, head and neck, but can occur over other areas of the body as well. Foamy macrophages and multinucleate histiocytic giant cells are seen within the dermis histopathologically. Impression smears or fine-needle aspirates from larger papules can contain these foamy macrophages as well. Complete evaluation of these cases should include evaluating cholesterol and triglyceride concentrations on a serum chemistry profile as well as screening for diabetes mellitus. Treatment is focused on reducing body fat. Diabetes should be controlled, and patients should be fed a low-fat diet. Resolution in most cases is achieved within 30 days.
Bowen's disease/squamous cell carcinoma in situ
Affecting older cats, this disease is thought to be a malignant transformation of viral papillomas causing lesions that are confined to the epidermis. The lesions are most commonly observed on the head, neck, dorsal thorax ventrum and legs, characterized by hyperkeratotic, pigmented macules and plaques. Shaving the cat in the regions of the lesions is advised to avoid missing early, mild lesions. Chronic lesions may have protruding keratin horns or may be ulcerated. Studies have shown that some cats can develop invasive squamous cell carcinomas in focal areas with this condition.
The disease is diagnosed based on results of a skin biopsy. The ideal treatment modality for squamous cell carcinoma in situ is a carbon dioxide laser. Complete ablation of the lesions is highly effective in many cases. Additionally, topical 5% imiquimod (applications in both human and equine medicine against lesions caused by papilloma viruses) can also be effective. Early detection and treatment are critical while lesions are confined to the epidermis.
Bronchogenic carcinoma with distant digital metastasis
Bronchogenic or squamous cell carcinomas of the lung in older cats can metastasize to the digits, resulting in the development of destructive lesions. Affected cats are commonly asymptomatic for the primary neoplasia. Usually multiple digits are involved on different feet. Diagnosis is based largely on radiography of the digits and thorax. Palliative treatment is recommended.
While rare, two paraneoplastic syndromes in cats can occur. An exfoliative dermatitis associated with thymomas occurs in middle-aged to older cats. Lesions consist of large crusting and advance rapidly. Diagnosis is based on skin biopsy, thoracic radiography, computed tomography and ultrasonography with fine-needle aspiration of the thymoma. Treatment involves mass removal (thymoma), which generally results in resolution of clinical signs. However, the condition can recur.
Paraneoplastic alopecia in cats with pancreatic or bile-duct carcinomas occurs on the ventral abdomen and legs. The affected skin appears smooth and shiny. These cats are often lethargic and anorectic. Biopsy of the affected skin reveals atrophy of the follicles. Diagnosis can be difficult and is based on ultrasonography with biopsy; in some cases, exploratory laparotomy is necessary to identify the tumor. Early diagnosis and treatment are critical to attempt tumor removal. However, by the time advanced skin lesions are present, the prognosis is grave.
Lymphocytic mural folliculitis
This immune-mediated condition is unique to cats. It is characterized by alopecia of the legs and face and can be treated with cyclosporine.
Degenerative mucinotic mural folliculitis
This preneoplastic condition is more sinister than its cousin lymphocytic mural folliculitis, causing generalized hair loss with thickened skin. It must be differentiated from T-cell lymphoma. Diagnosis is based on skin biopsy findings, and cats should be tested for FIV infection. Unfortunately, these cases do not respond well to treatment.
Dr. Blake is a freelance technical editor and writer in Eudora, Kan.