Eosinophilic keratitis and keratoconjunctivitis in a 7-year-old domestic shorthaired cat

Abstract

A 7-year-old, spayed female, domestic shorthair was presented with a several-month history of an ulcerated right cornea with marked stromal edema and inflammation that was nonresponsive to therapy. A diagnosis of eosinophilic keratitis was made, based on cytologic examination of corneal scrapings. The lesion resolved after treatment with topical corticosteroids.

A 7-year-old, spayed female, domestic shorthair was referred to the Ophthalmology Department of the Western College of Veterinary Medicine. It had a several month history of ulcerative keratitis in the right eye that was nonresponsive to treatment. On presentation, there was blepharospasm of the right eye, noticeable opacification and vascularization of the right cornea, and mild conjunctivitis. Neuro-ophthalmic examination revealed a negative right menace reflex. Pupillary light reflexes in the right eye could not be evaluated due to an extensive corneal infiltrate. Schirmer tear tests (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) were 19 mm and 24 mm in right and left eyes, respectively. Intraocular pressures were estimated with an applanation tonometer (Tonopen XL; Bio Rad Ophthalmic Division, Santa Clara, California, USA) and found to be 17 mmHg bilaterally. Both eyes were stained by using fluorescein sodium ophthalmic strips (Fluorets; Chauvin Pharmaceuticals, Romford, Essex, UK) by wetting the strips with eye wash solution, touching the strip to the bulbar conjunctiva just dorsal to the cornea, and allowing the cat to blink thus carrying the stain over the cornea. The right cornea retained stain over 80% of its surface when viewed in a dark room with a cobalt blue filter on a direct ophthalmoscope. The retention of stain indicated a break in the lipophilic corneal epithelium, demonstrating that the cornea was ulcerated.

Biomicroscopic examination confirmed an extensive right corneal ulcer with marked stromal edema and inflammation. A tentative diagnosis of eosinophilic keratitis and keratoconjunctivitis was made. Blood samples and swabs of the right cornea were submitted for polymerase chain reaction (PCR) evaluation for Herpesvirus, Chlamydia spp., and Mycoplasma spp. The samples tested positive for Mycoplasma spp. and Herpesvirus. The right cornea was scraped with the dull edge of a scalpel blade for cytological evaluation; this revealed a mixed population of cells, including neutrophils, mononuclear cells, and eosinophils. No microorganisms were noted with Wright-Giemsa staining. Thus, the tentative diagnosis was confirmed, and treatment of the right eye with topical 0.1% dexamathasone (Maxitrol; Alcon Canada, Mississauga, Ontario), 1 drop, q12h, was commenced.

The cat was examined again 24 h later to ensure that there was no bacterial component to the ulcer that could complicate the clinical progress under the corticosteroid treatment. There was noticeable clinical improvement. The inflammation, corneal edema, and size of the corneal ulcer had decreased. The topical 0.1% dexamethasone treatment was changed from 1 drop, q12h to 1 drop q6h.

The cat was reexamined at day 56 and showed signs of marked improvement. The results from the neuro-ophthalmic examination were now normal, and both eyes were negative on fluorescein staining. Biomicroscopic examination revealed multiple right corneal scars, minimal vascularization, and a mild follicular conjunctivitis. Due to the significant clinical improvement, the topical 0.1% dexamethasone treatment was decreased to 1 drop, q8h. Subsequently, this had to be changed back to 1 drop, q12h, as the keratitis appeared to be relapsing. At day 165, the keratitis was still being well managed on 1 drop of 0.1% dexamethasone, q12h.

Feline eosinophilic keratitis is a rare infiltrative and progressive keratopathy of the cat. The lesions are typically tan and have a granular or cobblestone appearance. They often originate from the limbus. Vascularization is commonly present and the unaffected cornea is frequently edematous (1). At the time of presentation, 24% of affected cats have a corneal ulcer in the affected eye. Conjunctival involvement is also commonly present and is indicated by thick hyperemic edematous conjunctiva (2). The disease seems to have no age, breed, or sex predilection and appears unilaterally 66% of the time (1). It has been suggested that as the disease progresses, it can become bilateral. Other presenting signs include ocular discharge, chemosis, blepharospasm, depigmentation of external eye lids, and thickening of the third eyelid (2). The differential diagnoses for feline eosinophilic keratitis include herpetic keratitis, keratomycosis, acid fast granuloma, corneal neoplasia, and foreign body granuloma (1,2).

Currently, feline eosinophilic keratitis is considered idiopathic; however, many possible etiologies have been speculated. Most of the debate has been over the relationship between feline eosinophilic keratitis and Feline herpesvirus. One study detected Feline herpesvirus in 76% of cases with eosinophilic keratitis (3), while in another study it was only 33% (1). The study showing a 76% correlation used more sensitive diagnostic tests. There has also been a suggestion that the cornea may be a depot for latent Herpesvirus (3).

Many authors have suggested that feline eosinophilic keratitis is linked to the feline eosinophilic granuloma complex, but this association has yet to be confirmed (3,4). Prasse (5) has suggested that the eosinophilic response could be explained by a type I or type IV hypersensitivity, but this theory has not yet been researched. It is currently believed that eosinophilic keratitis is related to feline eosinophilic conjunctivitis, another idiopathic syndrome observed in cats (5).

Feline eosinophilic keratitis is usually suspected when there is a history of no response to antibiotic treatment, along with the characteristic appearance of the lesions. Definitive diagnosis is made on cytologic examination of corneal scrapings, or light microscopy of corneal biopsies. The presence of eosinophils, eosinophilic granules, and mast cells in significant numbers is considered diagnostic for feline eosinophilic keratitis (1,2,6). Histologically, there is an associated mast cell and eosinophilic exocytosis. The superficial stroma of the cornea may be infiltrated by a variety of leukocyte types, and there is corneal epithelial hypertrophy, hyperplasia, and thinning (6).

The recommended initial treatment for feline eosinophilic keratitis is topical corticosteroids (1,2,6). Other suggested treatments include systemic corticosteroids and megestrol acetate (Ovaban; Schering-Plough Animal Health, Pointe Claire, Quebec). Topical corticosteroids is the first choice for treatment due to its efficacy, high local concentrations, and minimal side effects (7). Oral corticosteroids should not be used as a first line drug due to the high dosage needed for immunosuppression and the possible adverse effects. It has been suggested that megestrol acetate is useful in cats with a history of recurrent eosinophilic keratits (2). Megestrol acetate has been recommended, but it should be used cautiously, as it also causes adrenocortical suppression, is not licenced for use in cats, and has an 8-day half life (1,8). Recurrence rates for feline eosinophilic keratitis are high. Morgan et al (2) reported a recurrence rate of 64% in a study with 65 cats. Recurrence is reported with all treatment modalities.