A 32-year-old patient from South America with positive serology for Toxoplasma gondii presents with a focal necrotising chorioretinal lesion adjacent to a pigmented scar ('headlight in the fog' appearance). What is the mechanism of this classical fundus picture?
- A Reactivation of congenitally acquired Toxoplasma cysts in the retina adjacent to an old scar ✓
- B De novo primary ocular toxoplasmosis from environmental oocysts ingested via food
- C Haematogenous spread during acute acquired systemic toxoplasmosis
- D Immune-mediated retinal vasculitis triggered by Toxoplasma antigens
Correct answer: A. Reactivation of congenitally acquired Toxoplasma cysts in the retina adjacent to an old scar
Explanation
The classic 'headlight in the fog' or 'satellite lesion' of ocular toxoplasmosis represents an active, white fluffy necrotising lesion adjacent to an old pigmented chorioretinal scar—the result of reactivation of congenitally acquired Toxoplasma gondii bradyzoite cysts within retinal tissue. Reactivation is triggered by immune compromise or unknown stimuli. The scar indicates prior infection; the active lesion is the white fluffy area with overlying vitritis. Treatment with pyrimethamine + sulfadiazine + folinic acid is indicated for vision-threatening lesions.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.