Autoimmune Skin Lesions (Eosinophilic Granuloma Complex) in Cats

Key Takeaways

Eosinophilic granuloma complex is a condition characterized by the appearance of lesions on the skin in response to an allergen. 

• Eosinophils (a type of white blood cell) target the allergen in the blood, leading to a grouping of inflammatory cells (granuloma) that creates a large mass or lesion on the skin

• This type of lesion can be categorized into three broad types; eosinophilic granuloma, eosinophilic plaque, and indolent ulcer, which all appear visually different and are localized to different areas of the body

• While identification of eosinophilic lesions explains the immediate symptoms, it is not a specific diagnosis as the trigger needs to be determined

• Diagnostic tools include physical examination, medical history, bloodwork, and skin biopsies

• Once identified, treatment can be specific (dietary, flea treatment, laser therapy) or symptomatic (antibiotics, steroids)

A Closer Look: What is Eosinophilic Granuloma Complex in Cats?

This condition is uncommon in cats and broadly diagnosed. It can go away on its own, but if itching is persistent, it can lead to secondary infections. Treatment may take a while as the underlying allergen needs to be identified, but prognosis is good with careful monitoring and rapid intervention.

Risk Factors

Left untreated, eosinophilic lesions can develop into secondary infections.Cats that develop secondary infections may show symptoms such as:

• Tears in the skin and bleeding

• Inflammation around the affected area

• Oozing or discolored liquid indicating an infection

Cats with eosinophilic granulomas in the mouth may be irritated by the mass. These cats show symptoms such as:

• Avoidance of eating/drinking

• Pawing at the mouth

Excessive drooling

Symptoms are expected to recur until the underlying cause is identified.

Possible Causes

The cause of eosinophilic granuloma complex in cats is usually an allergic reaction, most commonly to a flea, mosquito, or mite bite. This can be triggered by a number of other allergens as well, including antibiotics, food allergens, and airborne pollen. Some cases have no identifiable allergen or underlying cause, and may be related to genetic predisposition.

Main Symptoms

The symptoms can be broadly separated into the three subtypes of the complex:

Eosinophilic Granuloma

• Raised, linear, clearly defined bumps (granules) on the skin

• Can vary in size from small bumps to large tumor-like masses

• Can be found anywhere on the skin, but primarily are seen on the mouth and hind legs

Eosinophilic Plaque

• Raised, red, irritated skin with hair loss

• Often seen on the abdomen, inner thigh, anal region, or throat

• Severely itchy

Indolent Ulcer

• Erosion of the upper lip from an ulcer like formation

• May also be seen on the tongue

Testing and Diagnosis

After a physical examination and medical history the vet may look at a few avenues for diagnosis, including:

• Skin biopsy (this is often to rule out other forms of lesion)

• Examination for parasites

• Bloodwork

• Visualization of cell samples from the lesions under a microscope

Steps to Recovery

Once the diagnosis is broadly made, treatment has two branches:


• Steroids to reduce inflammation

• Antibiotics

• Topical treatments

• Preventing further injury to the lesion through Elizabethean collars or protective clothing

Treatment of underlying causes

• Investigation of allergies to identify the trigger

• Food allergy diet

Flea/mite treatments

• Immunotherapy with injection of allergen into the skin

• Laser or cryotherapy

Female hormones used to be a common treatment option but are now used as a last resort due to potential side effects and long term risks.

This condition can clear up on its own or may require intensive treatment depending on the underlying cause and the overall health of the cat. Many cases wax and wane regardless of therapy, so recurrence is often expected even with treatment. 

Overall, the condition has a good prognosis and can be effectively managed. Patients on long-term therapy may require routine blood work to monitor for side effects of the medications.


The condition can not be fully prevented, but the probability of it occurring can be reduced by:

• Maintaining good hygiene

• Staying up to date on flea/mite treatments and vaccines

• Monitoring the environment and diet

Eosinophilic granuloma complex is not contagious.

Is Eosinophilic Granuloma Complex Common in Cats?

Eosinophilic granuloma complex is uncommon in cats.

Typical Treatment


• Steroids to reduce inflammation

• Antibiotics

• Dermal treatments


• Food allergy diet

• Flea/mite treatments

• Immunotherapy

• Laser or cryotherapy

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