Unraveling A Diagnostic Puzzle In A Patient With Rheumatoid Arthritis : Fungal Keratitis Vs Marginal Keratitis

Peripheral corneal ulcers can look strikingly similar regardless of their cause, making diagnosis a genuine clinical challenge. We report a case where a patient with rheumatoid arthritis presented with features strongly mimicking fungal keratitis, yet ultimately proved to have a sterile marginal ulcer. Our goal is to illustrate how careful clinical reasoning, microbiological workup, and anterior segment OCT can together unravel a deceptive picture and prevent unnecessary antifungal treatment.

Department of Ophthalmology. A 62-year-old female patient with a 10-year history of rheumatoid arthritis, previously treated with methotrexate (self-discontinued 3 years prior), presenting with acute visual loss and ocular inflammation in the right eye.

A 62-year-old woman with rheumatoid arthritis presented with sudden visual loss and redness in the right eye. Visual acuity was limited to finger counting. Slit-lamp examination revealed severe Meibomian gland dysfunction, conjunctival hyperemia, frothy secretions, and a superior pre-limbic crescent-shaped corneal ulcer with satellite infiltrates, corneal neovascularization, and diffuse corneal edema. Anterior segment OCT demonstrated corneal thinning and endothelial plaques, raising suspicion for fungal keratitis. Corneal microbiological sampling returned negative. Based on clinical features — significant blepharitis, limbal ulcer location, shallow depth, and negative cultures — the diagnosis of marginal keratitis associated with severe dry eye syndrome was established. Treatment with lubricating eye drops and doxycycline was initiated, alongside a rheumatology referral leading to systemic corticosteroid therapy (1 mg/kg/day). At 15-day follow-up, complete ulcer healing was observed, with resolution of endothelial plaques and restoration of endothelial regularity on OCT, confirming the sterile nature of the lesion.

Not every corneal infiltrate tells a straightforward story — and in patients with rheumatoid arthritis, marginal keratitis can convincingly masquerade as fungal infection, even on OCT. When the clinical picture is ambiguous, a structured approach combining slit-lamp examination, microbiological sampling, and anterior segment OCT is essential. A negative culture and a favorable response to lubricating drops and doxycycline are powerful diagnostic anchors. The systemic picture must never be overlooked — and when in doubt, scrape before you treat.