Microsporidial spores can cross the intact Descemet membrane in deep stromal infection.

We report a rare case of a deep stromal keratitis with a chronic indolent course, diagnosed as microsporidial keratitis from corneal scrapings. The patient's condition worsened despite medical therapy and penetrating keratoplasty was performed. The histopathology of the corneal tissue revealed multiple microsporidial spores in the posterior stroma and the endothelial exudates, whereas there was no clinical or histopathological breach in Descemet's membrane. This is the second report in the literature to report that micropsoridial spores can cross the intact Descemet's membrane.

INTRODUCTION

Microspordia are emerging pathogens in recalcitrant stromal keratitis.1 The disease is difficult to diagnose both clinically and by laboratory diagnosis. Existing reports have shown clinical and histological evidence that the disease is restricted to the stroma, with no recurrence after penetrating keratoplasty.12 Currently, there is little evidence demonstrating penetration into the anterior chamber (AC). We report a case of stromal microsporidial keratitis with presence of an intact Descemet membrane (DM) and demonstrable microsporidial spores in the AC exudates. This finding suggests the possiblity of recurrence of disease even after penetrating keratoplasty. This is only the second case to demostrate this rare finding.

CASE REPORT

A 26 year old healthy male presented on November 1, 2008 with a one-year history of recurrent redness, pain and watering in the right eye. The patient was a non-diabetic, with good general health and nutritional status. The condition waxed and waned despite multiple ophthalmology consults, and therapy that included topical antibiotics, corticosteroids and oral antiviral medication. Best-corrected visual acuity (BCVA) was counting fingers at one meter. Slit lamp examination showed intact, edematous epithelium, while the underlying stroma showed multiple, gray-white irregular to oval shaped flocculent infiltrates with indistinct borders; diffusely distributed over the entire cornea (except the limbus), involving the deep stroma [Figures 1a and b]. Endothelial exudates were also noted. The left eye was essentially normal.

Figure 1

(a and b) Slit lamp photographs showing the dense corneal infiltrates at presentation. (c) Persistence of stromal infiltrates three weeks after therapy. (d) Clear graft two months following penetrating keratoplasty

Corneal scrapings were obtained. The smear revealed multiple oval, spore-like structures, with a waist-band which was Gram positive, 1% acid fast positive and showed blue fluorescence on potassium hydroxide with calcofluor white stain, confirming a diagnosis of microsporidial stromal keratitis. Medical therapy was instituted with topical 0.02% chlorhexidine gluconate ever half-hour and oral albendazole 400mg twice daily; however here was no response even after three weeks [Figure 1c]. The patient underwent penetrating keratoplasty.

Surgery was performed under local anesthesia. A 9.5mm corneal graft was sutured with 16 interrupted sutures into a 10 mm recipient bed. The entire area of inflitrated corneal tissue was excised. Postoperatively, the patient was prescribed topical chlorhexidine 2% eight times a day (formulated in the hospital pharmacy) which was discontinued after three weeks, topical prednisolone acetate 1% eight times a day tapered over the next several months, and topical atropine sulphate 1% three times a day for two weeks. There was with no recurrence postoperatively. The visual acuity improved to 20/20 within two months [Figure 1d]. However, a year later, the patient presented with severe allograft rejection (he had stopped topical steroids) and subsequently the graft failed. An endothelial keratoplasty was performed and the patient was doing well at the last follow-up, two years postoperatively. The histopathology of the corneal button revealed an ulcerated cornea with dense inflammatory infiltrates in the stroma composed of neutrophils, lymphocytes and plasma cells with stromal necrosis. Numerous microsporidial spores were present in the deeper stroma upto the DM [Figures 2a–c] on Gram stain and 1% acid-fast stain. The DM itself was intact throughout the specimen. The AC exudates noted in some sections showed the presence of microsporidial spores [Figure 2d arrow].

Figure 2

(a) Section of the cornea shows epithelial ulceration, dense stromal infiltrates and AC exudates posterior to and separate from the DM (H and E, ×10). The DM is intact through the specimen. (b) 1% acid fast stain shows brightly stained microsporidial spores within the posterior stroma. (c) Under higher magnification (×100), the spores show the characteristic waist-band. (d) ×100 magnification with 1% acid fast stain showing presence of microsporidial spore (arrow) in the AC exudate

DISCUSSION

Microsporidial keratitis is an emerging, opportunistic clinical entity caused by parasites belonging to the genus microspora.1 Clinically the stromal form presents with mid to deep stromal infiltrate mimicking stromal HSV keratitis. Vemuganti et al, reported the largest series (five cases) of stromal microsporidial keratitis from this center that underwent penetrating keratoplasty, where the presentation ranged from stromal infiltrate to thinning with descemetocele formation.1 Interestingly, Font et al, reported a case of stromal microsporidial keratitis which had recurrence of infection following therapeutic DALK; requiring a penetrating keratoplasty.2 Das et al, recently reported a case of microsporidial keratits with the spores noted in the AC exudates.3 There have been reports on intraocular microsporidiosis causing endophthalmitis45 or sclero-uvetis with retinal detachment,6 however the mechanism of spread was presumed to be a systemic in these reports and none-of these patients had corneal involvement. With the current cases being reported, it is possible that the spread could have been through the intact ocular tissues rather than a hematologic route. Our case clearly demonstrates the presence of microsporidia in the AC exudates; which to our knowledge is the second case reported in literature. This finding may suggest a hitherto unknown, additional pathogenic mechanism of microsporidia with an ability to penetrate the intact DM (similar to fungi, under which these organisms have been reclassified7).

With an increasing trend towards DALK, it would be important to note that in the presence of endothelial exudates or AC exudates, a penetrating keratoplasty is preferred over lamellar keratoplasty, as the latter may be associated with recurrence of infection.