Chorioretinitis

Chorioretinitis refers to inflammation involving both the choroid (vascular layer) and retina of the eye, often resulting from hematogenous spread of infectious organisms. Key causes tested on USMLE include: (1) Toxoplasma gondii - classic cause of congenital chorioretinitis (triad with hydrocephalus and intracranial calcifications), also causes reactivation disease in AIDS patients (CD4 <100) presenting with focal necrotizing retinitis, often described as 'headlight in the fog' appearance; (2) Cytomegalovirus (CMV) - seen in severely immunocompromised patients (CD4 <50), classically described as 'pizza pie' or 'cottage cheese and ketchup' fundus appearance with hemorrhages and exudates, can lead to retinal detachment and blindness; (3) Congenital syphilis - causes 'salt and pepper' chorioretinitis; (4) Congenital rubella - also causes salt and pepper retinopathy; (5) Herpes viruses (HSV, VZV) - can cause acute retinal necrosis. Pathophysiology involves organism invasion of retinal/choroidal tissue leading to necrosis, inflammatory cell infiltration, and scarring. Clinical presentation includes blurred vision, floaters, photophobia, and eye pain; fundoscopic exam reveals yellow-white retinal lesions with overlying vitreous haze. Diagnosis is clinical with fundoscopy, supported by serology (Toxoplasma IgG/IgM) or PCR (CMV viral load, HSV/VZV PCR) of aqueous/vitreous fluid. Treatment depends on etiology: pyrimethamine-sulfadiazine-leucovorin for toxoplasmosis, ganciclovir/valganciclovir for CMV, acyclovir for HSV/VZV. In AIDS patients, chorioretinitis is an AIDS-defining illness and indicates need for antiretroviral therapy initiation. High-yield associations: TORCH infections, HIV/AIDS opportunistic infections, and differentiating CMV vs Toxoplasma retinitis based on CD4 count and fundoscopic appearance are frequently tested concepts.