Issues

Feline Eosinophilic Keratitis

 

Feline eosinophilic keratitis is a presumed immune-mediated inflammation of the cornea characterized by perilimbal corneal vascularization, white-pink corneal infiltrate, and corneal edema.

Synonym—proliferative keratitis.

 

SIGNALMENT

Young adult to middle-aged cats are most commonly affected.

 

SIGNS

• Unilateral or bilateral.
• Usually little to no ocular pain.
• Serous to mucoid ocular discharge.
• Limbal superficial corneal vascularization 90–360° (temporal or inferior nasal quadrants usually are first affected).
• White to pink flat or raised granular corneal infiltrate.
• Multifocal small white gritty corneal deposits.
• Corneal edema.
• With or without corneal ulceration.
• Conjunctival and third eyelid hyperemia, chemosis and thickening with or without a cobblestone texture to the surface.

 

CAUSES & RISK FACTORS

Feline herpesvirus-1 may be associated with FEK but the exact role is unclear: 76% of FEK specimens were PCR positive for FHV-1 in one study but 0% were positive in another.

The exact etiopathogenesis is unknown but proposed theories are: (1) Type I hypersensitivity with IgE mediated mast cell and eosinophil degranulation, (2) Type IV reaction where sensitized T-lymphocytes via IL-5 stimulate local eosinophil-mediated corneal damage.

Culture, histopathology, and electron microscopy have ruled out bacterial and fungal infection as consistent etiologic causes, although secondary bacterial keratitis may occur.

 

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

• Chronic corneal ulceration with secondary corneal vascularization (granulation tissue).
• FHV-1 stromal keratitis—appears similar to FEK but lacks the proliferative component, and more severe ocular pain and corneal ulceration are usually present.
• Corneal neoplasia: (1) lymphoma—concurrent conjunctival and/or uveal infiltration is common, (2) squamous cell carcinoma— rarely involves cornea in cats.
• Chlamydia psittaci or Mycoplasma felis—usually conjunctival diseases without corneal involvement.

 

CBC/BIOCHEMISTRY/URINALYSIS

Peripheral eosinophilia may be present.

 

OTHER LABORATORY TESTS

• Corneal cytology provides definitive diagnosis and should be done first. See numerous eosinophils, free eosinophil granules and/or mast cells, neutrophils, lymphocytes, plasma cells and epithelial cells.
• Cytology helps rule out chlamydia and mycoplasma.
• FHV-1 nested PCR—limited diagnostic value since normal healthy cats may carry FHV-1 and have positive PCR results.
• IFA testing for Chlamydia psittaci.
• Fluorescein staining to evaluate for corneal ulceration.

 

DIAGNOSTIC PROCEDURES

Keratectomy and histopathology may confirm a diagnosis in chronic or nonresponsive cases.

Specimens show epithelial cell layer hypertrophy and hyperplasia, corneal vascularization, excrescences with nuclear debris and amorphous eosinophilic material, numerous eosinophils, free eosinophil granules, deeper layers of thickened basement membrane and eosinophilic material and stromal thickening with eosinophils, mixed inflammatory cells and granulation tissue.

 

TREATMENT

Usually medical on outpatient basis.

 

MEDICATIONS

DRUG(S)

• Topical cyclosporine A q8–12h, then tapered to the lowest effective frequency of application and/or discontinued. Can use in cats in which megestrol and topical corticosteroids are contraindicated (diabetes, FHV-1, etc). May be irritating or cause blepharitis.
• Topical corticosteroids—1% prednisolone acetate or 0.1% dexamethasone sodium phosphate (initially q6–12h for 5–7 days, then gradually taper to the lowest effective frequency of application, q2–7 days). May eventually be discontinued in many cats.
• Adjunctive topical and/or systemic anti-viral therapy may be warranted in cases with history or clinical signs compatible with FHV-1 infection.
• Subconjunctival corticosteroids—triamcinolone acetonide (0.1–0.2 mL q3–7 days); use only in cats that are difficult to treat with topical medications.
• Megestrol acetate—2.5 mg PO q24h × 3–5 days, then 2.5 mg PO q48h × 3–5 days, then gradually decrease frequency after every 3–5 treatments to the lowest effective frequency (e.g., 2.5 mg PO q7 days) or eventually discontinue.
• Systemic prednisolone—start with 2.2 mg/kg PO q12h and taper. Use only if a cat will not tolerate topical corticosteroid or cyclosporine A therapy or megestrol acetate.

 

CONTRAINDICATIONS/POSSIBLE INTERACTIONS

Topical corticosteroid administration may be associated with recrudescence of FHV-1 keratoconjunctivitis and therefore should be used judiciously and monitored carefully. The client should be advised to immediately report any adverse change in the condition of the eye (blepharospasm, corneal edema, increased ocular discharge, etc.).

Megestrol acetate causes adrenal cortical suppression and may result in diabetes mellitus, polyphagia, temperament change, mammary gland hyperplasia, or neoplasia and pyometra. It should not be used in cats with hepatic disease or other illness.

 

FOLLOW-UP

Response to therapy is usually rapid.

Complete resolution may take several days to months. Many cats require long-term therapy to control the disease.

Corneal vascularization and infiltrate may resolve completely with minimal corneal scarring.

Recurrences in both the short and long term are common following discontinuation of therapy.

 

MISCELLANEOUS

FEK is not typically associated with the dermatologic eosinophilic granuloma complex.

 

ABBREVIATIONS

FEK = feline eosinophilic keratitis/keratoconjunctivitis

FHV-1 = feline herpesvirus-1

IFA = immunofluorescent antibody test

PCR = polymerase chain reaction

 

Visit your veterinarian as early recognition, diagnosis, and treatment are essential.

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