Cerebral toxoplasmosis in HIV — DTM&H MCQ

Correct answer: E — Cerebral toxoplasmosis

Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as E

Cerebral toxoplasmosis (C) is the most likely diagnosis. In a patient with untreated HIV and a CD4 count under 200 cells/microlitre (here 38), multiple ring-enhancing lesions with surrounding oedema, classically located in the basal ganglia, alongside subacute focal neurology such as hemiparesis and confusion, are the textbook presentation of toxoplasma encephalitis. Toxoplasmosis is the commonest cause of focal brain lesions in advanced HIV disease worldwide and this radiological pattern (multiple lesions, basal ganglia predilection, ring enhancement, oedema) is the discriminating feature that separates it from the other options. UK (BHIVA) practice is to start empirical anti-toxoplasma therapy (pyrimethamine/sulfadiazine or co-trimoxazole) and reassess clinically and radiologically at two weeks, reserving biopsy for those who fail to respond, which reflects how strongly this imaging pattern points to toxoplasmosis rather than requiring tissue diagnosis upfront. Why the other options are wrong: A. Tuberculous meningitis: presents with basal meningeal enhancement, hydrocephalus and cranial nerve palsies rather than multiple parenchymal ring-enhancing basal ganglia mass lesions; tuberculomas are usually single or fewer and less oedematous. B. Primary CNS lymphoma: typically produces a solitary or periventricular, subependymal lesion rather than multiple basal ganglia lesions, and is the key differential excluded by lesion multiplicity and thallium/PET or response to empirical anti-toxoplasma treatment. D. Cryptococcal meningitis: causes meningitic symptoms with raised opening pressure and CSF cryptococcal antigen positivity; CT typically shows meningeal changes or hydrocephalus, not multiple ring-enhancing parenchymal masses. E. Neurocysticercosis: lesions are usually smaller, at the grey-white junction, calcified in the chronic stage, and not specifically clustered in the basal ganglia with this degree of oedema in a patient this immunosuppressed. Key point: multiple ring-enhancing basal ganglia lesions with oedema in a patient with CD4 under 200 cells/microlitre is cerebral toxoplasmosis until proven otherwise, and empirical anti-toxoplasma therapy with clinical/radiological reassessment at two weeks is standard UK practice before biopsy.

Reference: BHIVA, Management of Opportunistic Infection in People Living with HIV (guideline, toxoplasmosis section), bhiva.org/clinical-guideline/OI-guidelines/