Acanthamoeba and Microsporidia Coinfection Causing Refractory Stromal Keratitis in an Immunosuppressed Patient: A...

To report a rare case of refractory stromal keratitis caused by coinfection with Acanthamoeba and microsporidia in a systemically immunosuppressed patient.

A 69-year-old woman with rheumatoid arthritis on systemic immunosuppressive therapy developed chronic keratitis after ocular trauma. Diagnosis was established through slit-lamp biomicroscopy, corneal scraping with modified trichrome and periodic acid-Schiff staining, culture on nonnutrient agar, polymerase chain reaction (PCR) with 18S rRNA gene sequencing, and in vivo confocal microscopy (IVCM). Treatment response and clinical outcomes were recorded.

Initial examination was consistent with microsporidial epithelial keratitis, which showed partial response to oral albendazole over 14 weeks. Progressive anterior-to-mid stromal infiltrates subsequently developed, refractory to antifungal therapy. Corneal scraping and IVCM demonstrated both microsporidial spores and Acanthamoeba cysts. Culture confirmed Acanthamoeba growth, and PCR with sequencing identified Acanthamoeba subgenotype T4B and Vittaforma corneae. Combination topical antimicrobial therapy led to ocular medicamentosa, and therapeutic penetrating keratoplasty was performed. Histopathology revealed residual microsporidial spores within keratocytes and degenerated Acanthamoeba cysts in the posterior stroma. At 3-month follow-up, the graft remained clear with no recurrence; best-corrected visual acuity was 20/125.

Coinfection with Acanthamoeba and microsporidia should be considered in immunocompromised patients presenting with atypical, treatment-resistant keratitis. Prompt and parallel diagnostic evaluation-including corneal scraping, IVCM, culture, and PCR-based pathogen identification-is essential. When medical therapy fails, therapeutic keratoplasty may be required. Early comprehensive diagnosis may prevent disease progression and need for surgical intervention.