Acute Retinal Necrosis (ARN)

Acute retinal necrosis (ARN) is a rare but serious condition that affects the retina, the light-sensitive layer at the back of the eye. ARN is caused by viral infections, most commonly herpes simplex virus (HSV) and varicella-zoster virus (VZV). However, other conditions can mimic ARN and should be considered in the differential diagnosis, including cytomegalovirus (CMV) retinitis, progressive outer retinal necrosis (PORN), syphilis, sarcoidosis, tuberculosis, and hemorrhagic occlusive retinal vasculitis (HORV).

CMV retinitis is a common cause of vision loss in patients with advanced immunosuppression, such as those with HIV/AIDS. It typically presents with bilateral retinal lesions and can be diagnosed with viral PCR from intraocular fluid.

PORN is a severe form of retinal necrosis typically caused by VZV. PORN typically presents with peripheral retinal necrosis, which rapidly progresses to involve the entire retina. A positive history of HIV infection, or immunosuppression should raise suspicion for PORN.

Syphilis can cause various ocular manifestations, including ARN-like retinitis. Ocular syphilis typically occurs in patients with late-stage syphilis and can be diagnosed with blood tests for syphilis antibodies.

Sarcoidosis is a systemic inflammatory disease that can involve various organs, including the eyes. Ocular sarcoidosis can present with various symptoms, including uveitis, optic nerve inflammation, retinal whitening and retinal vasculitis. A positive history of sarcoidosis or other autoimmune diseases should raise suspicion for ocular sarcoidosis.

Tuberculosis can cause various ocular manifestations, including ARN-like retinitis. Ocular tuberculosis typically occurs in patients with systemic tuberculosis and can be diagnosed with a positive tuberculin skin test or interferon-gamma release assay.

HORV is a rare but serious complication of cataract surgery with intracameral vancomycin. It typically presents with severe inflammation and necrosis of the retina and can lead to permanent vision loss. A positive history of recent cataract surgery with intracameral vancomycin should raise suspicion for HORV.

In conclusion, ARN is a rare but serious condition that can be caused by various viral infections. A thorough differential diagnosis is crucial to guide appropriate management.