Eosinophilic Granuloma Complex in Cats

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 eosinophils, neutrophils, plasma cells, and mononuclear cells predominating. Mild to moderate fibroplasia is common. Peripheral eosinophilia is not as common as in the eosinophilic plaque or the linear granuloma. Occasional cases due to pyoderma or dermatophytes have been reported; thus, a fungal culture of the surrounding hairs is recommended.

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.

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 in the oral cavity. When these lesions develop 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.

Hypersensitivity disorders (allergy to fleas, food, or inhalants) should be investigated by instituting strict flea control, testing for environmental allergens (intradermal or in vitro), and conducting 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 long-term management. Long-acting injectable methylprednisolone acetate should not be used more often than every 12 wk because of the potential to induce hyperadrenocorticism and/or diabetes mellitus. Cyclosporine (7 mg/kg/day) has been used successfully in the eosinophilic granuloma and plaque, less so in the lip ulcer. This may require laboratory monitoring (at least twice yearly) 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.