REFRACTORY KERATITIS: A MICROBIAL COCKTAIL OR INFECTIOUS ENIGMA?

To report an unusual case of chronic recurrent keratitis diagnosed as viral, bacterial and fungal at various stages in the course, wherein histopatholgy performed at the time of penetrating keratoplasty for visual rehabilitation revealed evidence of microsporidial keratitis.

Tertiary care eye hospital

A 39-year-old male patient underwent penetrating keratoplasty for visually significant corneal scarring in his right eye resulting from multiple episodes of infective keratitis over the course of nearly three years. Past ophthalmic history included secondary optic atrophy in other eye, and past medical history included chronic alcoholism with abstinence for over 3 years at the time of surgery. He initially presented to eye casualty with sudden onset painful blurring of vision in his right eye and was diagnosed and managed as herpetic disciform keratitis. The episodes kept recurring every few months despite oral acyclovir prophylaxis; though, they always responded well to therapeutic oral acyclovir and topical steroids. Few weeks after the third recurrence, he presented with secondary microbial infection with multiple stromal infiltrates on a background of previous stromal and endothelial scarring. In view of poor response to antibiotics, negative corneal scrapes and clinical appearance of dry infiltrates with feathery margins on a background of prolonged use of topical steroids, fungal keratitis was suspected and in-vivo confocal microscopy requested, which identified possible hyphae. Patient was thereafter treated with topical natamycin which resulted in resolution of keratitis over the next few weeks.

Unfortunately, he had a few more similar episodes, and in view of the recurrences, tear film sample was sent for viral PCR testing, which was interestingly positive for cytomegalovirus and negative for herpes simplex and herpes zoster virus. Baseline blood tests requested to rule out any underlying systemic pathology revealed normal full blood count, ESR, CRP, serum urea and electrolytes and fasting blood sugar along with negative HIV 1 & 2 and VDRL serology. Finally, histopathology of his cornea which was sent during penetrating keratoplasty revealed numerous tiny oval organisms positive for acid fast, Periodic acid–Schiff, and silver methanamine stains, consistent with a diagnosis of microsporidial stromal keratitis.

This case highlights an atypical presentation of microsporidial keratitis, which though relatively rare, is an important cause of keratitis in both immunocompetent and immunosuppressed individuals. In our case, it is difficult to say whether microsporidia were the causative organisms from the first episode, but it is more likely that they were acquired as a possible opportunistic infection later during the course. It is important to consider these organisms as a possible differential in stromal keratitis and to remember that they can mimic recurrent herpetic keratitis. High index of suspicion is needed for prompt diagnosis and treatment.