Pathology in Practice

Cesar Piedra-Mora Department of Biomedical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Sujata J. Desai Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Federica Maggio Tufts Veterinary Emergency Treatment and Specialties, Walpole, MA 02081.

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Samuel H. Jennings Department of Biomedical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Stephanie A. Pumphrey Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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History and Clinical and Gross Findings

A 12-year-old 8.9-kg (19.6-lb) castrated male Bichon Frise was presented for evaluation of the right eye 28 days after routine phacoemulsification was performed at another clinic (surgery performed on day 0). Corneal erosions had been noted in both eyes 24 hours after surgery. On day 5, debridement of both eyes with a sterile cotton-tip applicator was performed, followed by grid keratotomy and contact lens placement on day 9. Throughout this period, both eyes were treated topically with moxifloxacin, prednisolone acetate, nepafenac, dorzolamide, and 0.25% hyaluronan at various frequencies. Amoxicillin–clavulanic acid and prednisone were administered orally.

Acute, marked blepharospasm of the right eye was noted by the owner 26 days after surgery. Evaluation revealed a midstromal ulcer that affected most of the right corneal surface with severe keratomalacia (the erosion in the left eye had healed). Topical application of prednisolone acetate in the right eye was discontinued, and the topical medication regimen for that eye was modified to tobramycin, cefazolin, autologous serum, and hyaluronan 5 times a day; dorzolamide twice a day; and nepafenac 3 times a day. Oral treatment with doxycycline (5 mg/kg [2.27 mg/lb], q 12 h) was instituted for its anticollagenase effects.

On evaluation of the dog at our clinic on day 28, a malacic midstromal ulcer involving most of the right cornea was present (Figure 1). Neovascularization was budding from the limbus but had not yet reached the defect. Hypopyon and hyphema were present in the right eye; evaluation of the interior structures was not possible. Intraocular pressure of the right eye was 8 mm Hg. Menace response and dazzle and indirect pupillary light reflexes were assessed as present but diminished. Findings for the left eye were unremarkable in the context of patient history. Medications were continued unchanged.

Figure 1
Figure 1

Photographs of the right eye of a Bichon Frise that was evaluated 28 days after routine phacoemulsification (surgery performed on day 0). A—Image of the cornea on day 28 after fluorescein stain was applied to the eye. The axial cornea is opaque with an irregular contour and soft appearance consistent with severe malacia. B—Image of the cornea on day 35. The cornea is less opaque, and the borders of the ulcer appear crisp and well-defined. Neovascularization has progressed into the borders of the defect. A focal paraxial area of yellowed cornea is apparent. C—Image of the cornea on day 37. Notice the marked increase in opacity diffusely, along with much more conjunctival hyperemia and chemosis. Ventrally, the red tissue consists of hemorrhage and fibrin at the site of the corneal perforation.

Citation: Journal of the American Veterinary Medical Association 258, 8; 10.2460/javma.258.8.861

The dog was evaluated again at our clinic on day 35, and the condition of the right eye had improved. Hypopyon and hyphema were reduced, and the cornea was minimally malacic, with a remnant yellowed area located paraxially. Ulcer depth and size were unchanged. Neovascularization had progressed into the borders of the defect (Figure 1). Menace response and dazzle and indirect pupillary light reflexes were present. Intraocular pressure of the right eye was 12 mm Hg. Medications were continued, and a recheck evaluation of the dog in 7 days was planned.

The dog was presented emergently 2 days later (day 37) following a minor perceived trauma at home (contact between the Elizabethan collar and the right eye during collar replacement). The owner observed hemorrhage from the right globe after the incident. On evaluation, the cornea was diffusely malacic and edematous; there was a large paraxial perforation with hemorrhage and fibrin protruding from the cornea (Figure 1). Severe blepharospasm and chemosis were also noted. Owing to the dog's poor prognosis for vision and comfort, enucleation of the right eye was recommended. Routine transconjunctival enucleation was performed without incident, and the globe was submitted for histologic evaluation.

Histopathologic Findings

The enucleated right eye was fixed in neutral-buffered 10% formalin, routinely processed, and stained with H&E stain. Histologic examination revealed a perforated corneal ulcer with an extensive rupture in the Descemet membrane (Figure 2). The perforation was filled with fibrin and hemorrhage. The corneal stroma was edematous and infiltrated by degenerated neutrophils. The corneal stroma and Descemet membrane adjacent to the site of perforation contained numerous fungal hyphae that were 5 to 10 μm in width with parallel walls and acute-angle branching. With Gomori methenamine silver stain, the hyphae appeared black. Fibrin admixed with degenerated neutrophils and hemorrhage filled the anterior chamber. A thick preiridal fibrovascular membrane was multifocally adhered to the corneal endothelium (anterior synechiae). The ciliary body and iridal stroma were extensively infiltrated by neutrophils interspersed with fewer lymphocytes, plasma cells, and pigment-laden macrophages. The lens capsule was lined internally by a hyperplastic epithelium. Consistent with the recent phacoemulsification surgery, lens fibers were not seen. Macrophages surrounded the lens capsule. There was diffuse retinal detachment and hypertrophy of the retinal pigmented epithelium.

Figure 2
Figure 2

Photomicrographs of sections of the right globe after enucleation. A—The cornea is perforated centrally (asterisk), with extrusion of fibrin and inflammatory debris. Notice the linear band of connective tissue with surrounding inflammatory infiltrate and a disruption in the Descemet membrane at the right side of the image (dagger). This represents the previous surgical incision. The thicker bands of eosinophilic material at the bottom of the image are lens capsule remnants (arrows). H&E stain; bar = 2 mm. B—Higher magnification view of a section of the cornea outlined by the dashed rectangle in panel A. The corneal stroma adjacent to the perforation contains numerous neutrophils and 5- to 10-μm-wide fungal hyphae (arrowheads) with parallel walls and infrequent, acute branching that extend into the Descemet membrane (asterisk). Notice the fibrovascular membrane (double dagger) and inflammatory debris attached to the corneal endothelium. H&E stain; bar = 200 μm. C—After Gomori methenamine silver staining, fungal hyphae (arrowheads) within the corneal stroma and Descemet membrane (asterisk) are stained black. Gomori methenamine silver stain; bar = 50 μm.

Citation: Journal of the American Veterinary Medical Association 258, 8; 10.2460/javma.258.8.861

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: severe, extensive neutrophilic keratitis with corneal perforation and intralesional fungal hyphae and marked, diffuse neutrophilic and lymphoplasmacytic anterior uveitis.

Case summary: fungal keratitis with corneal perforation and severe reflex uveitis following cataract surgery in a dog.

Comments

Treatment for the dog of the present report was guided by the ultimately incorrect assumption that the melting ulcer in the right eye was either sterile or bacterial in origin. Index of suspicion for fungal keratitis was low owing to the dog's geographic location (New England) and time of year (December), lack of recent travel history, and initial improvement when treated with antimicrobials and anticollagenases. However, several risk factors for fungal keratitis were present for this dog, including recent ocular surgery, documented corneal ulceration, and recent topical corticosteroid and antimicrobial treatments.1,2,3,4,5,6,7

The rapid deterioration of the condition of the dog's right eye following initial improvement was concerning and prompted submission of the enucleated globe for histologic examination. In veterinary medicine, globes enucleated because of corneal perforations are often not submitted for histologic evaluation because the cause of the corneal perforation is presumed to be known and cost is a consideration. The case described in the present report underscored the value of histologic examination of enucleated globes; the findings not only explained the clinical course for this particular dog but also highlighted that fungal keratitis should be a differential diagnosis for companion animals regardless of geographic location. The latter is particularly pertinent for animals with known risk factors for fungal keratitis and those that have had poor responses to standard treatments for corneal ulceration.

Although common in horses and people, fungal keratitis is rare in dogs, with only 44 cases reported in the veterinary medical literature since 19748,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 to our knowledge. Fungal keratitis develops most commonly in animals located in areas with tropical or subtropical climates.1,2,3,4,5 Risk factors, in addition to those noted for the dog of the present report, may include ocular trauma, presence of foreign material in the cornea, disruptions to the corneal epithelium or tear film, and concurrent metabolic disease.1,3,4,5,6

Prompt diagnosis and early initiation of specific antifungal treatments are critical to the successful management of fungal keratitis in any animal species. In humans, fungal keratitis is much more likely to require surgical intervention or result in corneal perforation than bacterial keratitis, and prognosis is similarly guarded in horses with fungal keratitis.5,7,24 Invasion of the deep stroma and Descemet membrane by fungal organisms is a common finding in cases of fungal keratitis and was evident in the dog of the present report.25,26,27 Tropism for deeper corneal structures may be related to poorer outcomes in animals with fungal keratitis for multiple reasons, including inadequate penetration of topical medications to deeper portions of the cornea and direct damage to the Descemet membrane by fungal organisms or host defenses.

For the dog of the present report, enucleation was performed because of the poor prognosis for comfort and vision of the right eye and allowed a definitive diagnosis to be determined on the basis of histopathologic findings. Other potential means of diagnosis for fungal keratitis include cytologic examination, fungal culture, or PCR assay of appropriate ocular specimens and in vivo confocal microscopy.1,5,2830 Diagnostic techniques such as fungal culture or PCR assay may allow for more definitive fungal speciation than is possible with light microscopy alone.29,31 Speciation of the fungal organisms may guide treatment and contribute more accurate prognostic information.32 A PCR assay for use on formalin-fixed tissue specimens has been described but is not widely available. Use of that assay was not pursued in the case described in the present report because definitive treatment (ie, enucleation) had already been performed and fungal speciation was not considered necessary for further patient care.30,31,33

Acknowledgments

The authors received no financial support for the authorship of this article.

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