A 34-year-old HIV-positive man (CD4 count 90 cells/μL) has a 2-week history of left-sided weakness and headache. MRI shows a solitary ring-enhancing lesion in the left basal ganglia with surrounding oedema. Serum Toxoplasma IgG is negative and CSF PCR is strongly positive for Epstein-Barr virus DNA. What is the next best step?

• A Empirical pyrimethamine-sulfadiazine therapy and reassess at 2 weeks
• B Albendazole 400 mg twice daily for neurocysticercosis
• C Whole-brain radiotherapy before any tissue diagnosis
• D Stereotactic brain biopsy for histopathological confirmation ✓

Explanation

A solitary lesion with absent Toxoplasma IgG makes cerebral toxoplasmosis very unlikely, since over 80 percent of toxoplasmic encephalitis cases occur in seropositive patients. Detection of EBV DNA in CSF strongly suggests primary CNS lymphoma, an EBV-driven neoplasm of immunosuppressed patients. Because empirical antitoxoplasma therapy is reserved for multiple lesions in seropositive patients, tissue confirmation by stereotactic biopsy guides treatment, typically high-dose methotrexate-based chemotherapy.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.