Progressive outer retinal necrosis is a differential diagnosis for CMV retinitis.

Progressive outer retinal necrosis is a differential diagnosis for CMV retinitis.

• A. Histoplasmosis
• B. Progressive outer retinal necrosis
• C. Toxoplasmosis
• D. ARMD

Answer: (B)

In patients with severe immune suppression, CMV retinitis is a primary concern but progressive outer retinal necrosis (PORN) is an important differential because it can look similar at first glance. PORN is typically caused by varicella-zoster virus reactivation and tends to progress rapidly with necrosis that starts in the outer retina, often near the posterior pole, and spreads quickly. A key clue is the minimal inflammatory response in the eye—little vitritis and few overt inflammatory signs—despite extensive retinal necrosis. This contrasts with CMV retinitis, which classically presents as fluffy, full-thickness retinal necrosis along the vessels with hemorrhages and more inflammatory features giving a “pizza pie” appearance. Understanding these patterns helps distinguish PORN from others. Histoplasmosis retinochoroiditis usually shows chorioretinal scars and peripheral involvement rather than rapid outer retinal necrosis; toxoplasmosis presents as focal necrotizing retinochoroiditis with prominent vitritis and a characteristic active edge; age-related macular degeneration affects the macula in older individuals and involves drusen and neovascular changes rather than infectious necrotizing retinitis. So, PORN is the best differential to consider alongside CMV retinitis in the immunocompromised, aligning with the rapid outer retinal destruction and minimal inflammatory response.

In patients with severe immune suppression, CMV retinitis is a primary concern but progressive outer retinal necrosis (PORN) is an important differential because it can look similar at first glance. PORN is typically caused by varicella-zoster virus reactivation and tends to progress rapidly with necrosis that starts in the outer retina, often near the posterior pole, and spreads quickly. A key clue is the minimal inflammatory response in the eye—little vitritis and few overt inflammatory signs—despite extensive retinal necrosis. This contrasts with CMV retinitis, which classically presents as fluffy, full-thickness retinal necrosis along the vessels with hemorrhages and more inflammatory features giving a “pizza pie” appearance.

Understanding these patterns helps distinguish PORN from others. Histoplasmosis retinochoroiditis usually shows chorioretinal scars and peripheral involvement rather than rapid outer retinal necrosis; toxoplasmosis presents as focal necrotizing retinochoroiditis with prominent vitritis and a characteristic active edge; age-related macular degeneration affects the macula in older individuals and involves drusen and neovascular changes rather than infectious necrotizing retinitis.

So, PORN is the best differential to consider alongside CMV retinitis in the immunocompromised, aligning with the rapid outer retinal destruction and minimal inflammatory response.