In cats, 3 disease entities have been grouped in the complex.

Eosinophilic Ulcer

This well-circumscribed, erythematous, ulcerative lesion, often neither painful nor pruritic, is usually found on the upper lip. Some are associated with a hypersensitivity to flea bites. Although reported to occur, progression to squamous cell carcinoma is extremely rare. Histology shows an ulcerative dermatitis, with a cellular infiltrate of neutrophils, plasma cells, and mononuclear cells predominating. Mild to moderate fibroplasia is common. Tissue or peripheral eosinophilia is not as common as in the eosinophilic plaque or the linear granuloma.

Eosinophilic Plaque

This well-circumscribed, erythematous, raised lesion is most commonly found in the medial thigh and abdominal regions; it is extremely pruritic. Regional lymphadenopathy can be seen. Histology shows a diffuse eosinophilic dermatitis, with marked epidermal inter- and intracellular edema and vesicles containing eosinophils. Mast cells may also be present in the dermis. Peripheral eosinophilia is common.

Eosinophilic Granuloma

These typically raised, well-circumscribed, yellowish to pink lesions may be found anywhere on the body but are most common on the caudal thighs and oral cavity. When these lesions occur on the head, face, bridge of the nose, pinnae, or pads of the feet, mosquito bites may be the inciting cause. The caudal thigh lesions are usually distinctly linear. Histologically, a granulomatous inflammatory response surrounds collagen fibers. Tissue and peripheral eosinophilia are marked when the lesions are in the mouth but vary when lesions are on the skin.

Treatment

Hypersensitivity disorders (allergy to fleas, food, or inhalants) should be investigated by instituting strict flea control, allergy testing (intradermal or in vitro) and dietary elimination trials. Hyposensitization, continued insect control, and dietary management should be used when appropriate. Antibiotic therapy (amoxicillin-clavulanate, cephalosporins, or fluoroquinolones) should be tried empirically, especially in refractory cases. If no underlying cause can be determined and the condition is refractory, corticosteroids, such as methylprednisolone acetate (4 mg/kg, IM, once every 2 wk for 2–3 injections), oral prednisolone (2–4 mg/kg/day), or oral triamcinolone (0.8 mg/kg/day), can be tried. Oral corticosteroids should be tapered to alternate days (or to every third day in the case of triamcinolone), and dosages reduced when used for longterm management. Long-acting injectable methylprednisolone acetate should not be used more often than every 8–12 wk due to the potential for inducing hyperadrenocorticism and/or diabetes mellitus. Chlorambucil at 0.2 mg/kg, 3 times/wk, has also been used in refractory cases and requires more extensive blood monitoring due to its potential for bone marrow suppression; 6–12 wk may be needed before a response is seen, and the dosage and frequency should be reduced if response is seen. Cyclosporine (5 mg/kg/day) has been used in refractory cases. This may require monthly laboratory monitoring for metabolic (eg, renal) changes, although internal organ dysfunction is relatively rare. Progestational drugs, such as megestrol acetate or medroxyprogesterone acetate, have also been effective; however, they are not recommended because of their potential adverse effects.

Last full review/revision July 2011 by Stephen D. White, DVM, DACVD