Microsporidial stromal keratitis: treatment outcomes, clinical manifestations, confocal microscopy and histopathology findings: a retrospective observational study

Objective Microsporidial stromal keratitis (MSK) is an uncommon disease. Only several case series have been reported. We aimed to describe the clinical manifestations, histopathology and treatment outcomes of MSK. Methods and analysis Retrospective data of MSK diagnosed between January 2009 and December 2020 at the King Chulalongkorn Memorial Hospital, Bangkok, Thailand were retrieved. The diagnosis was made based on corneal scraping, corneal biopsy and corneal button histopathology findings. Detailed clinical characteristics, histopathological findings and treatment outcomes were reviewed and analysed. Results 21 patients with MSK with a mean age of 63.8 years (SD 12.2) had an indolent disease onset with a median of 9 months (IQR 2.2–12.0). Five patients (23.8%) experienced ocular traumas. Herpes stromal keratitis was the most common preliminary diagnosis (33.3%), followed by non-specific ulcers and fungal keratitis. The most common corneal finding was multifocal grey-white lesions with anterior to mid-stromal infiltration and fluffy borders (66.7%). Pathogens were identified by modified trichrome staining of corneal scrapings in 11 of 14 cases (78.6%). Histopathological examination showed positive Ziehl-Neelsen staining in 17 of 19 cases (89.5%). All patients received surgical treatment, with 18 receiving therapeutic penetrating keratoplasty (TPK), 2 undergoing deep anterior lamellar keratoplasty and 1 undergoing femtosecond laser-assisted anterior lamellar keratoplasty. The overall cure rate was 76.2% after the first surgery and 95.2% after the second surgery. Conclusion MSK can be easily underdiagnosed. Clues to diagnosis included a history of chronic refractory stromal infiltration and typical corneal findings of deep stromal infiltration, without epithelial defects. TPK is the preferred treatment for MSK.