Case Report: Presumed ocular tuberculosis masquerading as acute retinal necrosis: the diagnostic and therapeutic journey of an elderly female.

BACKGROUND: Acute retinal necrosis (ARN) is typically caused by varicella-zoster or herpes simplex virus, but Mycobacterium tuberculosis can present an identical clinical picture. Distinguishing tuberculous uveitis (TBU) from ARN is challenging when etiological tests are unavailable. CASE PRESENTATION: A 78-year-old woman presented with rapid visual loss (hand motion) in the left eye. Examination revealed elevated intraocular pressure, mutton-fat keratic precipitates, severe anterior chamber and vitreous inflammation, retinal arteritis, and peripheral necrotic lesions, which met the 2015 Japanese diagnostic criteria for presumed ARN with undetermined virology. Standard antiviral therapy (famciclovir, two intravitreal ganciclovir injections, and corticosteroids) failed to halt the progression. An interferon-gamma release assay (IGRA) was positive, and chest CT showed non-specific changes. After discontinuing antivirals, diagnostic anti-tuberculosis therapy (ATT) led to rapid improvement: visual acuity reached 0.1, inflammation resolved, and necrotic lesions became pigmented scars. Over a 12-month follow-up period, which included 6 months of observation after completion of ATT, the patient maintained a stable BCVA of 0.1, with no evidence of retinal detachment or disease recurrence. The final diagnosis was revised to presumed ocular tuberculosis. CONCLUSION: Presumed ocular tuberculosis can clinically mimic ARN. When suspected ARN progresses despite adequate antiviral treatment, intraocular tuberculosis should be included in the differential diagnosis. When a definitive diagnosis cannot be established, an ATT trial guided by indirect evidence such as a positive IGRA is a reasonable clinical option. It should be clarified that this trial only supports a presumptive diagnosis rather than a definitive diagnosis.