Unilateral choristoma of the nictitating membrane in a horse

• Autores: Kara R. Gornik
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 246, Nº. 2, 2015, págs. 231-235
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • Case Description—A 2-year-old Morgan mare was evaluated because of a corneal ulceration.

    Clinical Findings—An irregular, deep stromal corneal ulcer in an area of malacia was noted in the left eye. Hypopyon was present in the ventral portion of the anterior chamber with moderate aqueous flare. The nictitating membrane of the left eye had hairs originating from its leading edge that contacted the corneal surface.

    Treatment and Outcome—General anesthesia was induced, and a bulbar pedicle conjunctival graft was performed. The conjunctiva at the leading edge of the nictitating membrane, including the aberrant hair follicles, was excised. Microscopically, a nonkeratinized stratified squamous epithelium, sebaceous glands, and hair shafts were present, confirming a choristoma of pilosebaceous origin at the leading edge of the nictitating membrane. Six weeks after surgery, the horse had no signs of discomfort, with no regrowth of the hairs; no loss of vision was evident.

    Clinical Relevance—Ocular choristomas develop secondary to defective fetal cellular differentiation and are rarely reported in the equine literature. The choristoma in this horse contained ectopic hair follicles with hair growth as well as sebaceous glands. This finding emphasizes the importance of a thorough adnexal examination in horses with corneal disease.

    A 2-year-old 379-kg (834-lb) female Morgan horse was evaluated because of a nonhealing corneal ulcer in the left eye. The mare had a history of possible trauma to the eye several weeks prior to referral; this had initially been treated by the referring veterinarian with topical administration of neomycin-polymyxin-dexamethasone ophthalmic ointmenta and atropine ophthalmic ointment,b along with systemic administration of flunixin megluminec (1.0 mg/kg [0.45 mg/lb], PO, q 12 h) for presumed anterior uveitis. On recheck examination 1 week later, a superficial corneal ulceration of the affected eye was noticed by the referring veterinarian. The horse was subsequently hospitalized, and a subpalpebral lavage catheter was placed in the superior conjunctival fornix. Topical treatment was changed to ofloxacin,d 1% voriconazole,e autogenous serum, and atropine ophthalmic solution.f Administration of flunixin megluminec was continued. The horse was referred to the veterinary teaching hospital several days later because of exacerbation of the corneal ulceration and development of grossly visible intraocular inflammation.

    On examination, the horse had marked blepharospasm of the left eye. Results of an ophthalmic examination included normal menace responses and dazzle reflexes bilaterally. Palpebral reflexes were normal in both eyes. Direct and indirect pupillary light reflexes were normal in the right eye but absent in the left. Following visual testing, an auriculopalpebral nerve block was performed with 2 mL of 2% lidocaine hydrochloride.g An approximately 10 × 6-mm irregular stromal corneal ulcer (with approximately 75% stromal loss at its deepest aspect) in an area of malacia was observed in the dorsomedial aspect of the left cornea. Corneal neovascularization was present, extending from the dorsal and medial aspects of the limbus and approaching the nasal (ventromedial) edge of the ulcer. The cornea surrounding and lateral to the defect was edematous and malacic.

    Several hairs were observed to originate from the leading edge of the nictitating membrane of the left eye, contacting the medial surface of the cornea and touching the innermost aspect of the corneal ulcer (Figure 1). Hypopyon was present in the ventral portion of the anterior chamber. Moderate aqueous flare was detected. The left pupil was nearly maximally dilated. No remarkable anterior segment abnormalities were found in the right eye. A well-demarcated area (3 × 3 mm) of decreased pigmentation was present ventral to the optic nerve in the nontapetal fundus of the right eye. This finding was consistent with a posterior segment coloboma involving the retinal pigmented epithelium and underlying choroid. Fundic examination was not attainable in the left eye because of the severity of the corneal disease and intraocular inflammation.

    View larger version(30K) Figure 1— Photograph of the left eye of a 2-year-old Morgan mare evaluated because of a corneal ulceration. A—A large, irregular corneal ulceration with edema and malacia is present in the dorsomedial region of the cornea, with blood vessels extending from the dorsal and medial aspects of the limbus. Intraocular inflammation and hypopyon are evident. B—Enlarged image of the outlined region in Panel A. Two hairs can be seen emanating from the leading edge of the nictitating membrane (arrows).

    Diagnostic testing included aerobic bacterial and fungal cultures, cytologic evaluation of a sample obtained by corneal scraping, and a CBC and serum biochemical analysis. Coagulation assessment, comprising measurement of fibrinogen concentration, prothrombin time, and activated partial thromboplastin time, was performed because the horse had a history of epistaxis following nasogastric tube placement while hospitalized under the care of the referring veterinarian. Aerobic bacterial culture results consisted of 1+ growth (scale, 1+ to 4+) of Streptococcus zooepidemicus, which was susceptible to all antimicrobials tested. Fungal culture yielded 1+ growth of Candida spp. Cytologic findings were consistent with severe neutrophilic inflammation. Degenerate and nondegenerate neutrophils were present, along with epithelial cells. No fungal organisms or intracellular bacteria were detected cytologically. The CBC results were within respective reference ranges. Serum biochemical abnormalities included low concentrations of magnesium (1.4 mEq/L; reference range, 1.8 to 3.0 mEq/L), total protein (3.7 g/dL; reference range, 5.6 to 7.0 g/dL), albumin (2.2 g/dL; reference range, 2.4 to 4.0 g/dL), and globulin (1.5 g/dL; reference range, 2.5 to 4.9 g/dL). Prothrombin time (10.4 seconds; reference range, 10.9 to 14.5 seconds) and activated partial thromboplastin time (50.2 seconds; reference range, 54.7 to 69.9 seconds) were both low, indicating more rapid clot formation times. A fast localized abdominal sonography evaluation was performed because of low serum protein concentrations and a history of reduced manure production. The horse had moderate thickening of the right dorsal colon, consistent with mild right dorsal colitis.

    The horse was hospitalized for stabilization overnight. Treatments included topical application of autogenous serum (0.2 mL, q 2 h) and ophthalmic preparations of ofloxacind (0.2 mL, q 4 h), 3.3% cefazolinh (0.2 mL, q 4 h), 1% voriconazolee (0.2 mL, q 6 h), and atropinef (0.2 mL, q 12 h) via the subpalpebral lavage catheter. Systemic treatment with flunixin megluminei (1 mg/kg, IV, q 12 h), sulfamethoxazole-trimethoprimj (30 mg/kg [13.6 mg/lb], PO, q 12 h), fluconazolek (14 mg/kg [6.4 mg/lb], PO, once), omeprazolel (4.6 mg/kg [2.1 mg/lb], PO, q 24 h), misoprostolm (1 μg/kg, PO, q 12 h), ranitidinen (6.6 mg/kg [3 mg/lb], PO, q 8 h), and sucralfateo (22 g/kg [10 g/lb], PO, q 6 h) was initiated. Water was also administered frequently via a nasogastric tube.

    The following day, the serum total protein concentration was considered to be stable at a value of 4.0 g/dL. General anesthesia was induced. An auriculopalpebral nerve block, supraorbital nerve block, and retrobulbar block were performed with 2% lidocaine hydrochloride.g The cornea was debrided, and the malacic tissue was removed and submitted for histologic evaluation. A bulbar pedicle conjunctival graft was harvested from the dorsomedial conjunctiva and sutured over the ulcerated region of the cornea with 8–0 polyglactin 910p in a simple interrupted pattern.

    The conjunctiva on the leading edge of the nictitating membrane, including associated hair follicles, was excised (Figure 2). Care was taken to avoid damage to the underlying cartilage of the nictitating membrane. Hemorrhage was controlled with cellulose spongesq and 2.5% phenylephrine solution.r The resultant wound was left to heal by second intention. The excised conjunctival tissue containing the hairs was submitted for histologic examination.

    View larger version(28K) Figure 2— Photograph of the nictitating membrane of the left eye of the horse in Figure 1 at the time of surgery. Four aberrant hairs (arrows) are seen extending from the leading edge of the left nictitating membrane.

    Anesthetic recovery was uneventful, and the horse remained hospitalized for 7 days following surgery. The PCV and circulating total solids concentration were evaluated daily. Continued treatment included topical administration of autogenous serum (0.2 mL, q 6 h), ofloxacin (0.2 mL, q 6 h), cefazolin (0.2 mL, q 6 h), 1% voriconazole (0.2 mL, q 6 h), and atropine (0.2 mL, q 12 h) via the subpalpebral lavage catheter. Systemic administration of flunixin meglumine, sulfamethoxazole-trimethoprim, omeprazole, misoprostol, ranitidine, and sucralfate was continued at the previously described dosages, and the fluconazole dosage was reduced (5 mg/kg [2.3 mg/lb], PO, q 24 h). Flunixin meglumine administration was discontinued 5 days after admission, and administration of firocoxibs (0.2 mg/kg [0.09 mg/lb], PO, q 24 h for 2 days, then 0.1 mg/kg [0.04 mg/lb], PO, q 24 h) was initiated because of sustained low serum total protein concentration (4.8 g/dL) as well as increased serum creatinine concentration (from 1.8 mg/dL [reference range, 0.9 to 1.9 mg/dL] on admission to 2.2 mg/dL 5 days after admission).

    Results of the histologic examination of the corneal biopsy sample were consistent with the cytologic findings and consisted of stromal infiltration by neutrophils, lymphocytes, plasma cells, and macrophages. No bacterial or fungal organisms were observed with H&E stain or with Gömöri methenamine silver stain. Histologically, the leading edge of the nictitating membrane contained a noncornified stratified squamous epithelium, sebaceous glandular tissue, follicular epithelium, and hair shafts (Figure 3).

    View larger version(50K) Figure 3— Photomicrographs of conjunctival tissue obtained from the leading edge of the nictitating membrane. A—An ectopic hair follicle (asterisk) with surrounding sebaceous glandular tissue (dagger) can be seen within the submucosa. B—A hair shaft (arrow) is present within an ectopic hair follicle located on the leading edge of the nictitating membrane. H&E stain; bar = 60 μm.

    Ophthalmic examination 7 days after surgery indicated that the graft was well vascularized with focal areas of bruising (Figure 4). The surrounding cornea remained mildly edematous. The pupil was fully dilated, and the intraocular inflammation largely resolved. The total protein concentration remained moderately low at 5.0 g/dL. The serum creatinine concentration returned to a normal value of 1.4 mg/dL. The horse was discharged from the hospital, and the owner was given instructions to administer autogenous serum, ofloxacin, cefazolin, 1% voriconazole, and atropine topically via the subpalpebral lavage catheter at the same dosages used after surgery. Systemic administration of firocoxib (0.1 mg/kg, PO, q 24 h) omeprazole (dose reduced to 1.15 mg/kg [0.5 mg/lb], PO, q 24 h), fluconazole, misoprostol, and sucralfate (at previously described dosages) was continued. Systemically administered antimicrobials were changed from sulfamethoxazole-trimethoprim to minocyclinet (4.0 mg/kg [1.8 mg/lb], PO, q 12 h) owing to its anticollagenolytic and anti-inflammatory properties.

    View larger version(35K) Figure 4— Postoperative clinical photograph obtained 7 days after surgery. The graft and sutures were in place at the dorsomedial aspect of the cornea. Corneal neovascularization was still present dorsally. There was moderate bruising in the center of the graft, and the edges remained well vascularized. Mild corneal edema was still visible lateral to the graft site. The intraocular inflammation had largely resolved, and the pupil was fully dilated. The nictitating membrane had healed with no visible hairs extending from its leading edge.

    Follow-up conversations with the referring veterinarian 6 weeks after discharge confirmed that the horse had no detectable visual defects and had no signs of discomfort in the left eye. The graft was not trimmed because of its medial location and presence outside of the visual field. No regrowth of hairs was noted on the leading edge of the nictitating membrane.