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CNS Lymphoma — SCE Infectious Diseases MCQ

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HardCNS InfectionCNS LymphomaSCE Infectious Diseases

A 42-year-old man with well-controlled HIV on DTG/TAF/FTC develops new-onset seizures. MRI brain shows multiple ring-enhancing lesions with surrounding oedema, predominantly at the grey-white matter junction. His CD4 count is 580 cells/µL and has been >350 for 5 years. Toxoplasma IgG is negative. What is the most likely diagnosis?

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Correct answer: E — CNS lymphoma or alternative non-Toxoplasma aetiology; proceed to stereotactic biopsy

Ring-enhancing lesions in HIV are classically attributed to Toxoplasma encephalitis, but this diagnosis is highly unlikely when Toxoplasma IgG is negative (NPV >95% for excluding Toxoplasma in HIV patients) and the CD4 is well-preserved (>500). In a Toxoplasma IgG-negative patient with high CD4, the differential shifts toward primary CNS lymphoma, brain abscess, or metastatic disease. Stereotactic brain biopsy is indicated for definitive diagnosis rather than empirical anti-Toxoplasma therapy.

Reference: BHIVA 2022 – OI guidelines; NICE NG99 2018 – Brain tumours