Feline Cutaneous Reaction Patterns: Eosinophilic Granuloma Complex, Non Inflammatory Alopecias and Miliary Dermatitis - Part I of II
By: Rada Panich, DVM, Dip. ACVD Chairperson, Dept of Dermatology
There are several common feline cutaneous reaction patterns that are associated with a wide range of different underlying skin diseases.The most common ones are eosinophilic granuloma complex, miliary dermatitis, head/neck pruritus and non inflammatory symmetrical alopecia. There is a tendency to define the reaction pattern of the pruritus rather than determine the underlying etiology of the lesions.Eosinophilic Granuloma (EGC)
Eosinohilic granuloma complex is not a specific diagnosis and the primary cause should be identified in order to establish effective long-term management therapy. There are four main types of EGC lesions that have distinct clinical features and unique dermatohistopathologic findings. The most common underlying causes include flea bite hypersensitivity, atopic dermatitis, adverse reactions to food, feline demodicosis, Cheyletiella, ectopic Otodectes ear mites, dermatophytosis and less commonly bacterial infections. Cutaneous nonepitheliotropic or epitheliotropic lymphoma may clinically resemble EGC when it presents as firm plaques, erosions and ulcers in arciform or serpiginous shapes typically affecting the inguinal area. Evaluation of surface cytology and skin biopsies are useful in order to differentiate these conditions. A distinct subtype of EGC may appear as a firm swelling affecting the rostral aspect of the chin ("fat chin" or "chin edema") and/or the lower lip ("pouting lip").
A. Cutaneous eosinophilic granuloma
Cutaneous eosinophilic granuloma is typically localized on the caudal aspect of one or both hind limbs or the medial aspect of the forelegs . It appears as a raised, linear, firm, well circumscribed and infiltrated lesion approximately 0.5 to 5 cm long. Less commonly, it may be found on the dorsal aspect of the nose, forelimbs, thorax and neck. In some patients, only the footpads and interdigital skin may be affected with erosions, ulcers and crusts. Immune-mediated diseases such as pemphigus foliaceus and plasma cell pododermatitis may clinically resemble cutaneous eosinophilic granuloma.
B. Eosinophilic ulcer
These lesions are also referred to as 'rodent ulcers' or 'indolent ulcers' and are typically found as unilateral or bilateral ulcers occurring on the upper lip near the philtrum or adjacent to the upper canine teeth. The elevated lesional margins are firm and have a pink to yellow or whitish central ulcerated area. In some patients, the ulcer may resemble squamous cell carcinoma and skin biopsies with histopathologic evaluation of tissue are advised. Lesions may be solitary and unilateral or they can become confluent and involve the entire upper lip area with significant firm perilesional swelling. The feet and oral cavity may also be affected, although this is an uncommon distribution pattern. Despite their aggressive appearance, feline eosinophilic lip ulcers are typically not pruritic or painful.
C. Eosinophilic plaque
Eosinophilic plaques are intensely pruritic, solitary or multiple, well circumscribed, moist, raised/ infiltrated lesions commonly affecting the ventral abdomen and medial thigh areas that may be accompanied by a peripheral lymphadenopathy. Surface cytologic evaluation of exudate reveals numerous eosinophils, neutrophils and occasionally staphylococcal bacteria due to the exudative nature of the lesions and development of secondary pyoderma. Dermatohistopathology findings include hyperplastic, superficial and deep perivascular to diffuse eosinophilic dermatitis with occasional microabscesses. Complete blood counts often show peripheral eosinophilia.
D. Oral eosinophilic granuloma
These lesions appear as erythematous nodules or plaques with gritty, pale, white foci affecting the hard or soft palate, tongue, or frenulum. Multiple lesions often coalesce. Owners frequently report anorexia, hypersalivation, dysphagia and halitosis.
E. Mosquito-bite hypersensitivity
A seasonal pattern of recurrence associated with exposure to mosquitoes characterizes mosquito-bite hypersensitivity. Multiple small pinpoint papules on the dorsal muzzle develop into erosions, ulcerations and crusts frequently causing moderate to intense pruritus. Lesions may also appear in the sparsely haired pre-auricular region and caudal pinnae. Severe, superficial to deep eosinophilic inflammation or infiltrative mural folliculitis and furunculosis are reported on histopathology.
Since eosinophilic granuloma complex dermatoses present as fairly distinctive skin lesions, it is tempting to establish a diagnosis based on clinical appearance and disregard other possible diseases with a similar presentation. Differential diagnoses to consider are squamous cell carcinoma, epitheliotropic lymphoma, mast cell tumors, lymphosarcoma, herpes or calici virus associated ulcers and mosquito-bite hypersensitivity. Infectious granulomas caused by cryptococcus, mycobacteria and nocardia may also clinically resemble EGC lesions.
Evaluation of these patients begins with a detailed review of the history which is useful in determining the cause of the cutaneous reaction patterns. Patient age at time of onset of lesions, history of excessive scratching or grooming, clinical response to prior therapy, distribution pattern of lesions, seasonal recurrences, presence of other animals in the household, possible exposure to fleas, and a comprehensive dietary history should be established.
The minimum data base for a cat with non-inflammatory alopecia, miliary dermatitis, head / neck pruritus, and eosinophilic granuloma complex includes surface and deep skin scrapings, clear acetate tape smears, fine-tooth combings and a trichogram. Fungal cultures are more reliable than Wood's lamp examination and should be routinely performed in kittens, young cats, recently adopted animals, indoor/outdoor pets, older debilitated cats as well as patients treated with chemotherapy drugs. A direct impression smear and cytologic evaluation of exudate is an inexpensive, simple procedure that yields valuable information about inflammatory cell types (eosinophils, neutrophils, macrophages, acantholytic keratinocytes), infectious organisms such as bacteria or yeast or presence of acantholytic keratinocytes. The only reliable diagnostic method to determine the role of adverse reactions to dietary allergens is a strict hypoallergenic using a novel or hydrolyzed protein for a period of 12 weeks. The owner is instructed to refrain from giving the cat any other commercial food, table scraps, treats or flavored supplements during that time. The choice of protein selected is based on a detailed history of prior exposure, and for most cats, rabbit or venison is an excellent choice. Hydrolyzed protein diets may also be used, and although it has not been conclusively demonstrated, these diets may be less reliable in diagnosing adverse reactions to dietary allergens. A relapse of pruritus following re-exposure to previous diets is an important step in confirming food allergies and ruling out other variables. Pruritus typically recurs within 2 to 14 days following re-exposure. Only one food item should be re-introduced per week, so that should a flare-up of inflammation occur, the specific dietary allergen can be easily identified. In vitro or intradermal allergy testing for foods is not recommended due to the well-established unreliability of these tests, despite which, most commercial laboratories continue to offer that option for testing for food allergies.
Allergy testing and allergen specific immunotherapy is the treatment of choice for long-term management of atopic dermatitis. Atopy and food hypersensitivity are the most common causes of feline symmetric alopecia, eosinophilic granuloma complex and miliary dermatitis in our geographic area, assuming that exposure to fleas has been definitively ruled out.
Part II of this article will include a discussion of differential diagnoses, and therapeutic management of feline eosinophilic complex, miliary dermatitis and feline symmetrical alopecia.