The most common manifestation of congenital toxoplasmosis is_____?

Correct Answer: A. Chorioretinitis

Chorioretinitis is the most common single manifestation of congenital toxoplasmosis, occurring in 70–80% of symptomatic cases. This is the discriminating fact that separates it from other features of the classic triad (hydrocephalus, intracranial calcifications, chorioretinitis). The pathophysiology involves Toxoplasma gondii crossing the placental barrier and establishing tachyzoite infection in fetal tissues, with particular tropism for the retina and choroid. The infection causes focal necrotic lesions with surrounding inflammation, classically described as "cotton-wool scarring" or "salt-and-pepper retinopathy" on fundoscopy. In Indian pediatric practice, congenital toxoplasmosis is less common than in Western countries due to lower maternal seroprevalence, but when diagnosed (typically via PCR on amniotic fluid or neonatal serology), chorioretinitis is the hallmark finding that prompts long-term ophthalmologic follow-up. The lesions may be active (white, fluffy) or inactive (pigmented scars), and can progress throughout childhood if untreated. Spiramycin (given to mother) or pyrimethamine + sulfadiazine + folinic acid (given to neonate) are the Indian DOCs, with the goal of preventing progression of retinal disease.

Why the other options are wrong

B. Hydrocephalus — Hydrocephalus occurs in only 10–15% of congenital toxoplasmosis cases and is part of the classic triad but not the most common manifestation. It results from aqueductal stenosis or obstruction by intracranial calcifications, making it a secondary consequence rather than a primary tissue tropism. NBE pairs hydrocephalus with toxoplasmosis to trap students who memorize the triad without understanding frequency hierarchy. C. Thrombocytopenia — Thrombocytopenia is a hematologic manifestation seen in 5–10% of cases, typically as part of a TORCH syndrome picture with hepatosplenomegaly and jaundice. It reflects placental infection and bone marrow involvement but is far less specific and less common than chorioretinitis. This option exploits confusion between TORCH features. D. Hepatosplenomegaly — Hepatosplenomegaly occurs in 10–20% of symptomatic congenital toxoplasmosis and is a sign of systemic dissemination and placental inflammation. However, it is not the most common single organ manifestation—ocular involvement dominates. This option is a distractor for students who conflate TORCH hepatitis with the primary pathology of toxoplasmosis.

High-Yield Facts

Mnemonics

TORCH Manifestations Frequency Chorioretinitis (most common in toxo) > Hydrocephalus > Hepatosplenomegaly. Remember: Ocular disease dominates toxoplasmosis; systemic signs are secondary. Congenital Toxo Triad (but know the hierarchy) Chorioretinitis + Intracranial calcifications + Hydrocephalus = CIH. But chorioretinitis alone is 70–80% of cases; the full triad is rare. Don't assume all three are equally common.

NBE Trap

NBE exploits the "classic triad" mnemonic by offering hydrocephalus as a distractor. Students who memorize the triad without understanding frequency distribution often choose hydrocephalus, forgetting that chorioretinitis is far more common and often occurs in isolation.

Clinical Pearl

In Indian neonatal screening, any newborn with positive toxo serology and a normal head ultrasound should still undergo dilated fundoscopy before discharge—chorioretinitis may be the only sign, and early detection prevents progressive vision loss. Many cases are asymptomatic at birth but develop active retinitis in childhood.

_Reference: OP Ghai (Pediatrics) Ch. 10 (Infectious Diseases); Harrison Ch. 218 (Toxoplasmosis)_