Microsporidia-induced stromal keratitis: a new cause of presumed immune stromal (interstitial) keratitis

To describe the clinical features, diagnosis and management of immune stromal keratitis/interstitial keratitis (IK) associated with microsporidial epithelial keratitis.Between October 2020 and January 2021, medical records of IK patients microbiologically proven as microsporidia from samples collected from corneal epithelium on smear examination, and/ or molecular analysis were reviewed. Demography, clinical profile and treatment were analysed. Real-time PCR (RT-PCR) for adenovirus (ADV), Epstein-Barr virus (EBV), herpes simplex virus (HSV) and varicella-zoster virus (VZV) was done.Twenty of 152 (13%) microbiologically proven cases of microsporidial keratitis were diagnosed as IK during the study period, the mean age and duration of symptoms were 35.7±11.4 years and 46.3±27.7 days, respectively. Half had predisposing risk factors, like trauma; and 30% had prior recurrences. One-fourth of patients were using antivirals on presentation. Characteristic presentations included disciform keratitis(n=12), incomplete/complete ring(n=5), and combination(n=3), along with variable subepithelial infiltrates (n=14). All cases had stromal oedema, with an intact epithelium and fine pigment dusting on endothelium. Corneal epithelial scrapings had scanty microsporidia spores in smears of 17/20 (85%), and pan-microsporidial DNA was identified in 14/20 (70%), with Vittaforma corneae by sequencing in 11/20 (55%). Other viruses detected were ADV (14,70%), VZV (2,10%), EBV (1,5%) and HSV (1,5%). Rapid resolution of inflammation and oedema within 2 weeks of starting steroids was seen in all cases.Microsporidia epithelial keratitis induced stromal inflammatory keratitis; is distinguished from microsporidial keratoconjunctivitis and stromal keratitis, by characteristic clinical features, and response to topical steroids.