Cats are affected by three eosinophilic skin diseases: eosinophilic ulcer (indolent ulcer), eosinophilic plaque, and focal eosinophilic granuloma. Because an individual cat may be affected by more than one of these skin diseases simultaneously, these diseases are sometimes referred to as a complex. Hypersensitivity reaction to an allergen (eg, insect, environmental, adverse food reaction) is the most common underlying cause. In some cases, the underlying trigger is unknown.
Eosinophilic Ulcer in Cats
An eosinophilic ulcer, also known as an indolent ulcer or rodent ulcer, is a well-circumscribed, unilateral or bilateral, erosive to ulcerative lesion most commonly present on the dorsal lips (see eosinophilic ulcer images, classic and less common presentations).
Indolent ulcers are typically associated with allergic skin diseases in cats, particularly flea bite hypersensitivity, but can be observed in some cats with environmental or adverse food reactions. Indolent ulcers can also develop as a result of inflammation (eg, trauma).
Courtesy of Dr. Karen Moriello.
Courtesy of Dr. Karen Moriello.
Eosinophilic ulcer diagnosis is based on clinical signs, and its presence should trigger a workup for parasitic and environmental allergies. Lesion evaluation should include the following steps:
trichogram (to assess for Demodex mites)
impression smear
Wood's lamp examination
dermatophyte culture (in at-risk cases)
Biopsy is indicated if there is no response to appropriate treatment or if the lesion develops suddenly and is destructive. If the lesion is present unilaterally, other oral neoplasia should be considered.
Eosinophilic Plaque in Cats
Eosinophilic plaque is an intensely pruritic exudative lesion that can occur anywhere on a cat's body (see exudative lesion image). It is the result of self-trauma from pruritus.
Courtesy of Dr. Karen Moriello.
The most common triggers of eosinophilic plaque are flea bite hypersensitivity and allergic skin disease due to environmental or adverse food reactions; this is one manifestation of feline pyoderma.
Treatment is with systemic antimicrobials, based upon culture and susceptibility. Flea control should be instituted or reevaluated. Recurrent lesions are the hallmark of underlying allergic skin diseases.
Cytological examination shows eosinophilic and neutrophilic exudation. Histological examination shows 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 with eosinophilic plaques.
Focal Eosinophilic Granuloma in Cats
Focal eosinophilic granulomas, also called collagenolytic granulomas, are characterized by firm nodules in the skin. Unlike eosinophilic ulcers or plaques, these are truly granulomas. Lesions can occur anywhere on the body.
The most common trigger is insect bite hypersensitivity.
Lesions on the ears are common in cats with mosquito bite hypersensitivity.
Chin and lip lesions (known as fat chin) are common in cats with flea bite hypersensitivity.
A variant known as a linear granuloma (often bilateral pencil-like thickenings on the caudal thighs) has become less common in the US, presumably due to the widespread use of flea preventatives. Flea bite hypersensitivity is an underlying trigger (see eosinophilic granuloma image).
Courtesy of Dr. Karen Moriello.
Histologically, a granulomatous inflammatory response surrounds collagen fibers.
Tissue and peripheral eosinophilia are marked when eosinophilic granulomas are in the mouth but vary when lesions are on the skin.
Lesions will resolve when the underlying trigger is treated.
Treatment of Eosinophilic Skin Diseases in Cats
Eosinophilic skin conditions are not diseases per se, but rather clinical signs. The presence of these lesions should alert the clinician to look for common causes of allergy in the cat, the most common being flea bite hypersensitivity. Thorough treatment with flea preventatives should be started and maintained for 2–4 months.
Pearls & Pitfalls
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Lip ulcers and exudative lesions often improve with concurrent antimicrobial therapy based upon culture and susceptibility, which should be the first treatment approach. Empirical antimicrobial therapy should not be used.
If lesions do not resolve with aggressive flea control and antimicrobial therapy, anti-inflammatory dosages of prednisolone (1–2 mg/kg, PO, every 24 hours until resolution) or triamcinolone acetate (0.05–0.1 mg/kg, PO, every 24 hours for up 10 days) can be administered. Resolution can take several weeks.
Cats with recurrent lesions may have feline hypersensitivity disorder, and testing for environmental allergens and/or a food trial may be indicated. Rarely, an underlying trigger cannot be identified, and feline cyclosporine modified oral solution (7 mg/kg, PO, every 24 hours until resolution) can be helpful.
For More Information
Buckley L, Nuttall T. Feline eosinophilic granuloma complex (ities): some clinical clarification. J Feline Med Surg. 2012;14(7):471-481.
Brooks W. Eosinophilic granuloma complex in cats. Veterinary Partner (VIN).
Also see pet owner content regarding eosinophilic lesions in cats.
