Cerebral toxoplasmosis — DTM&H MCQ

Correct answer: C — Pyrimethamine, sulfadiazine and folinic acid

The correct answer is C, pyrimethamine, sulfadiazine and folinic acid, because this presentation (CD4 count 70 cells/mm3, focal weakness, multiple ring-enhancing basal ganglia lesions on CT) is classic for cerebral toxoplasmosis, the commonest intracranial mass lesion in untreated HIV with CD4 below 100 to 200 cells/mm3. Toxoplasma gondii reactivates from latent cysts once cell-mediated immunity fails, producing necrotising encephalitis with basal ganglia predilection and multiple ring-enhancing lesions. Pyrimethamine and sulfadiazine act synergistically on the parasite folate pathway, with folinic acid given to prevent pyrimethamine-induced marrow toxicity without blocking the antiparasitic effect. In resource-limited settings, empirical therapy is started on clinical and radiological grounds, and clinical improvement within 10 to 14 days is used diagnostically when biopsy is unavailable. Why the other options are wrong: D. High-dose fluconazole monotherapy: this treats Cryptococcus, which causes meningitis with a normal or hydrocephalic CT, not multiple ring-enhancing basal ganglia lesions. E. Albendazole and praziquantel: this treats neurocysticercosis, which typically shows small calcified or cystic lesions at the grey-white junction, not the acute multifocal basal ganglia pattern described. A. Ceftriaxone and metronidazole alone: this empirical bacterial abscess regimen has no activity against Toxoplasma, and pyogenic abscess is far less likely given the CD4 threshold and imaging pattern. B. Immediate whole-brain radiotherapy: this is reserved for primary CNS lymphoma once toxoplasmosis is excluded by failed response to an anti-toxoplasma trial, never given empirically first. Key point: In HIV with CD4 under 100 to 200 cells/mm3 and multiple ring-enhancing basal ganglia lesions, empirical pyrimethamine, sulfadiazine and folinic acid is started first, with clinical response confirming the diagnosis.

Reference: i-base, HIV Treatment for All / UK HIV Treatment Guide, section 5.11 Toxoplasmosis: pyrimethamine, sulfadiazine and folinic acid for six weeks as first-line therapy for cerebral toxoplasmosis (https://i-base.info/ttfa/5-ois-and-coinfections/11-toxoplasmosis/); consistent with BHIVA guidelines on management of opportunistic infection in people living with HIV.