February 12, 2018

ACVC 2017: Understanding Skin Disease in Cats

Although much remains unknown about feline dermatology, one thing is certain: Many skin conditions are related to internal disease.
By JoAnna Pendergrass, DVM
Cutaneous Herpes Virus Infections
This condition typically affects older cats (8 to 9 years old) and can cause ulcerative and necrotizing facial dermatitis. The nasal planum, bridge of the nose, and periocular skin are commonly affected. Histopathologic findings include ulcerated epithelium, intranuclear inclusion bodies in keratinocytes (indicating herpes virus infection), multinucleated giant cells and keratinocytes in the surface and follicular epithelium, and interstitial mixed inflammatory dermatitis with eosinophils.

Systemic antibiotics are indicated to treat secondary bacterial infections, and acyclovir can help treat the viral infection. Corticosteroids can activate the virus and thus are not recommended for treating cutaneous herpes virus infections. Lysine has been proposed as a treatment option but, according to Dr. Sousa, hasn’t shown much efficacy. Human alpha-interferon is another option for treating cutaneous herpes virus infections, but cats eventually develop antibodies to it, making it less effective over time. None of the treatment options will get rid of the herpes virus carrier site within an affected cat’s body, Dr. Sousa said.

Multicentric Squamous Cell Carcinoma In Situ (Bowen Disease)
Bowen disease affects cats older than age 10 years and is triggered by papillomavirus. This slowly progressive disease causes eroded crusted papules and plaques that are frequently found on the head and neck but can also appear on the shoulders and forelegs. This disease is not solar induced and does not metastasize.

To obtain a diagnosis, Dr. Sousa recommended taking a 6-mm punch biopsy of the dermis and epidermis; epidermal abnormalities, she warned, may prevent proper skin healing. To remove the sting of lidocaine, she advised adding sodium bicarbonate (0.9 mL lidocaine, 0.1 mL bicarbonate) to the local anesthetic. She also suggested prerinsing the syringe with epinephrine to reduce bleeding. Epidermal dysplasia without basement membrane destruction is apparent on histopathology.

Surgical laser excision is the preferred treatment, with radiation and systemic retinoids recommended as adjunctive therapies. Vitamin A therapy may be useful for keratinocyte proliferation.

Miscellaneous Diseases
Indolent Ulcer (“Rodent Ulcer”)
Indolent ulcer.

This skin disease has no age, sex, or breed predilection. Well-circumscribed, red-brown ulcers with raised borders usually form on the upper lip. Interestingly, ulcers are neither eosinophilic nor granulomatous on histopathology; peripheral eosinophilia may be present.

Chronic, excessive licking due to allergic or pruritic stimuli is thought to cause the ulcers. If the ulcers are recurrent or refractory, Dr. Sousa recommended testing for food allergies or flea allergy dermatitis.

Early treatment is best; however, systemic glucocorticoids are often ineffective. Systemic antibiotics and progestational drugs can be useful in refractory cases. Treatments such as cryosurgery and laser therapy are primarily cosmetic, Dr. Sousa said.

Eosinophilic Granuloma
The clinical description of this lesion varies with location. Eosinophilic granulomas are ulcerated on the lips or within the oral cavity (back of palate, palatal arches); on the caudal thigh, the granulomas are linear, raised, circumscribed, and yellow-to-pink plaques. On histopathology, eosinophils are attached to the collagen.

Linear granulomas can regress spontaneously. Granulomas on the lips or within the oral cavity can be treated with steroids.

Eosinophilic Plaques
This common feline skin condition also is not associated with a particular age, sex, or breed. Affected cats are extremely pruritic and resort to excessive licking and grooming, causing plaques. Most often there is an underlying allergic skin disease. The ulcerated lesions are typically found on the abdomen and medial thighs and are well circumscribed, raised, round or oval, and erythematous. Many cats have a circulating peripheral eosinophilia.

Treatment is the same as for indolent ulcers.

Plasma Cell Pododermatitis
This rare condition has no known etiology. Initially, the lesions, which frequently affect the central carpal or tarsal footpads, are soft and painless with loss of the surface architecture. Over time, the pads become ulcerated and develop secondary infections, causing pain, lameness, and regional lymphadenopathy. Affected cats are otherwise healthy.

Histopathology provides a definitive diagnosis. Spontaneous regression occurs occasionally, while other cases benefit from systemic glucocorticoid or prednisolone treatment; response begins within about 3 weeks and peaks within about 3 months. Tetracycline or doxycycline (5 mg/kg twice daily) can also be used. Surgical excision is recommended for ulcerated footpads to improve healing and prevent recurrence.

Injection-Site Panniculitis
Subcutaneous injections of rabies vaccine, praziquantel, and methylprednisolone acetate have reportedly caused panniculitis in the dorsal cervical region and midscapular area. Occurring several months after injection, the skin reaction can range from inflammation and alopecia to ulceration and fat necrosis.

Disease management can be difficult. Treatment options include intralesional or systemic glucocorticoids, identification and treatment of underlying allergies, and surgical excision.

Self-Induced Alopecia (“Fur Mowing”)
Affected cats often present with partial, symmetric, or complete alopecia on areas accessible to licking. Excessive licking may be due to a psychological disorder or underlying allergy. Trichograms of the distal hair tips will help demonstrate that the alopecia is self-induced.

If allergic and inflammatory conditions have been ruled out, medical treatment options—all oral—include phenobarbital (1-2 mg/kg once or twice daily), amitriptyline (5-10 mg/day), and buspirone (0.5 mg/kg/day), which may be also useful for psychogenic alopecia.

Dr. Pendergrass received her DVM from the Virginia-Maryland College of Veterinary Medicine and completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. She is the founder and owner of JPen Communications, LLC, a medical communications company.

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