Successful Management of a Rare Keratitis Caused by Mycobacterium Immunogenum After a Series of Misdiagnoses

This case report presents the successful diagnosis and management of a rare case of Mycobacterium immunogenum keratitis. A 34-year-old immunocompetent female presented with a 6-month history of recurrent right eye redness and blurred vision. Previous treatment at other hospitals with oral antivirals, topical corticosteroids, and ganciclovir ointment for presumed herpetic keratitis had failed, with progressive vision decline from 20/20 to 20/50. The causative pathogen identification revealed Mycobacterium immunogenum through comprehensive diagnostic workup including microbiological culture, acid-fast staining, and metagenomic next-generation sequencing (mNGS). Initial therapy with topical amikacin proved ineffective and caused significant ocular toxicity, whereas adjunctive oral azithromycin showed no clinical benefit. Subsequent treatment with 0.3% gatifloxacin eye gel resulted in dramatic improvement. During the healing phase, 0.02% fluorometholone was added to control scarring. Complete resolution was achieved within 4 months, with only mild residual scarring and final uncorrected visual acuity of 20/30. The patient remained recurrence-free throughout 4 years of follow-up. This case demonstrates that Mycobacterium immunogenum keratitis does not necessarily occur in immunocompromised individuals or those with a history of trauma or surgery. It is easily misdiagnosed in the early stages, whereas mNGS can aid in pathogen identification. Treatment with 0.3% gatifloxacin eye gel suggests potentially superior efficacy and safety in such condition.