Toxoplasma encephalitis — DTM&H MCQ

Correct answer: D — Pyrimethamine with sulfadiazine and folinic acid

Pyrimethamine with sulfadiazine and folinic acid is correct because this presentation (advanced HIV with CD4 well below 100 cells/mm3, focal neurology, headache, fever, and multiple ring-enhancing lesions in the basal ganglia) is the classic pattern of cerebral toxoplasmosis, the commonest HIV-associated focal brain lesion at this level of immunosuppression. Toxoplasma gondii reactivation causes necrotising encephalitis, and the basal ganglia and grey-white junction are the typical sites for the multiple ring-enhancing lesions seen on imaging. UK guidance recommends pyrimethamine plus sulfadiazine as first-line treatment, with folinic acid co-prescribed to prevent pyrimethamine-induced bone marrow suppression, given for six weeks before switching to secondary prophylaxis. Empirical anti-toxoplasma therapy is started on clinical and radiological grounds without waiting for serology or biopsy, and a therapeutic response confirms the diagnosis. Why the other options are wrong: A. Fluconazole: This is an antifungal used for cryptococcal meningitis, which typically causes meningitis with raised opening pressure rather than focal ring-enhancing mass lesions, and does not treat toxoplasma. B. Praziquantel: This treats neurocysticercosis and schistosomiasis; cysticercosis lesions are usually small cystic lesions with a scolex, not the multiple basal ganglia ring-enhancing pattern of toxoplasmosis, and praziquantel has no activity against Toxoplasma gondii. E. Albendazole: This is used for neurocysticercosis and other helminth infections; it has no role in treating toxoplasma encephalitis and would not be first-line for this imaging and clinical picture. C. Cefalexin: This is a first-generation cephalosporin with no central nervous system penetration and no activity against Toxoplasma gondii, so it has no role here. Key point: In a patient with advanced HIV (low CD4 count) and multiple ring-enhancing basal ganglia lesions, treat empirically for cerebral toxoplasmosis with pyrimethamine, sulfadiazine and folinic acid.

Reference: BHIVA Guidelines for the treatment of opportunistic infection in HIV-seropositive individuals (2011, chapter 2.5 Toxoplasmosis), as summarised by HIV i-Base: https://i-base.info/ttfa/5-ois-and-coinfections/11-toxoplasmosis/