Feline eosinophilic granuloma complex

This is an umbrella term for various lesions that affect the skin, mucocutaneous junctions, and oral cavity of cats, and includes a clinical and histological description of the skin's response to an underlying or idiopathic cause.

Feline eosinophilic granuloma complex basically consists of three types of clinically and histologically different lesions that can appear simultaneously in a single animal:

• Indolent ulcer (eosinophilic ulcer, rodens ulcer or atonous ulcer)
• Eosinophilic plaque
• Eosinophilic granuloma (linear or collagenolytic granuloma)

The aetiology is unclear, although there are certain predisposing factors, such as genetic factors, sex (it is more common in females) or even coat colour (white or partially white cats). Determinants include allergic diseases (food allergies, atopy, hypersensitivity to flea and mosquito bites), bacterial or viral infections, stress and psychogenic factors (excessive licking).

Symptoms

Indolent ulcer: The age of onset varies between 9 months and 9 years. The ulcer is red or dark brown in colour, unilateral or bilateral, well circumscribed, alopecic, ulcerated and inflamed with raised borders. It generally occurs on the upper lip, near the philtrum, or adjacent to the upper canine teeth, although they can sometimes appear on the lower lip, in the oral cavity, and very rarely on the skin. The ulcer is not itchy or painful. In some cases it is associated with peripheral lymphadenopathy, and very rarely it can develop into squamous cell carcinoma or fibrosarcoma.

Eosinophilic plaque: These plaques appear in animals between 2 and 6 years of age. They typically consist of a raised, shiny, alopecic area with eroded, exudative red patches that are poorly defined and vary in size. They usually appear on the belly, thighs, or in the groin and perineal area, although they sometimes occur in the oral cavity, the edge of the eye, the conjunctiva, the axilla, or high on the foreleg. They may be associated with peripheral lymphadenopathy. These lesions are extremely itchy.

Eosinophilic granuloma: a raised linear or nodular, alopecic, yellowish pink lesion that appears in cats between 6 months and 5 years old. It is usually located on the caudal aspect of the rear leg, and initially appears as a linear lesion that evolves into focal or multifocal nodules that may ulcerate. Lesions may also occur on the chin, ears, the top of the head, and even in the oral cavity, including the tongue (nodular form). They may be associated with peripheral lymphadenopathy. They are not itchy.

Recommended analysis

Differential diagnosis:

• Indolent ulcer: infectious ulcer / injury / chemical, thermal or electrical burn / cancer (squamous cell carcinoma, mast cell carcinoma, lymphoma).
• Eosinophilic plaque and eosinophilic granuloma: bacterial-fungal granulomas / feline eosinophilic syndrome / cancer (squamous cell carcinoma, mastocytoma, lymphoma).

Interpretation of laboratory tests

General Tests

• Complete blood count: The most significant finding is peripheral eosinophilia, which is very common in eosinophilic plaque, common in eosinophilic granuloma, and rare in indolent ulcer.
• Bacterial culture / Fungal culture (dermatophytes): Cultures (of correctly obtained samples) are either negative or the isolated microorganisms are commensal.
• Scrape cytology: Skin scrapings are used to rule out external parasites (demodex), while imprint or aspiration cytology may reveal the presence of eosinophils, mast cells, and other inflammatory cells (especially in plaques and granulomas). Although these findings are inconclusive, they can guide diagnosis.

Specific tests

• Histopathology.
  Skin biopsies confirm the diagnosis of eosinophilic plaques and granulomas, but are less useful in the case of indolent ulcers since the histopathological lesion is non-specific.
  Histopathological characteristics of the lesions.
  • Ulcer:
    epidermis: parakeratosis / acanthosis / ulceration. Dermis: polymorphic infiltrate (plasmacytes, neutrophils, rarely eosinophils and mast cells) / fibrosis.
  • Plaque:
    epidermis: spongiosis / eosinophilic microabscesses / erosion / ulceration. Dermis: massive infiltration of eosinophils and mast cells.
  • Granuloma:
    epidermis: moderate hyperkeratosis: polymorphic infiltrate (eosinophils, mast cells, histiocytes) / collagenolysis / giant cells.
• Allergy testing.
  This should be performed if the disease is suspected to be due to an allergic reaction.
  Skin tests (intradermal): useful for diagnosing reactions to environmental allergens (dust mites, flea saliva, various pollens). Although this is the standard test, it has several drawbacks: a significant number of false positives, variable results, unreliable reproducibility, subjective interpretation of reactions, and non-standardized allergen sources.
  In vitro quantification of specific IgEs: same utility as the previous test, less traumatic for the animal, and more standardised. It is important to use a method that detects only allergen-specific IgEs (on FcεRI receptors) (1) in order to avoid false positives.
  Elimination diet (food allergy): if a food allergy is suspected. An over-the-counter hypoallergenic diet with a novel or hydrolysed protein may be used for at least 10-14 weeks.

(1) - Allercept®.

Bibliography

• BARDAGI, M.; FONDATI, A.; FONDEVILA, D.; FERRER, L.: (2003) Veterinary Dermatology vol.14(6), pg. 297-303.
• FONDATI, A.; FONDEVILA, D.; FERRER, L.: (2001) Veterinary Dermatology vol. 12(6), pg. 333-338.
• GUNTER, M.J. (2004) : en Morgan-Bright-Swartout (Ed.): Clínica Veterinaria de Pequeños Animales (4ª ed.) Saunders-Elsevier, pg. 864-867
• SCOTT, D.W.; MILLER, W.H.; GRIFFIN, C.E. (2001): En Muller&Kirk (Ed.): Small Animal Dermatology (6ª ed.) W. Saunders, pg.1148-1153
• TAGLINGER, K.; HELPS, C.R.; DAY, M.J.; FOSTER, A.P.: (2005) Veterinary Immunology and Immunopathology vol. 105 (1-2), pg.85-93.
• WISSELINK, M.A.; VAN REE, R.; WILLEMSE, T.: (2002) American Journal Veterinary Research vol. 63(3), pg. 338-341.