A 45-year-old man presents with progressive headache for 3 months, papilloedema, and a ring-enhancing lesion with surrounding oedema on contrast MRI. He is HIV-positive with CD4 count 80 cells/μL. What is the MOST likely diagnosis?
- A Glioblastoma multiforme — most common primary brain tumour
- B CNS toxoplasmosis — empirical pyrimethamine/sulfadiazine therapy first ✓
- C Cerebral abscess — neurosurgical drainage required immediately
- D Primary CNS lymphoma — needs brain biopsy
Correct answer: B. CNS toxoplasmosis — empirical pyrimethamine/sulfadiazine therapy first
Explanation
In an HIV-positive patient with CD4 <200 cells/μL and a ring-enhancing brain lesion, CNS toxoplasmosis (due to Toxoplasma gondii reactivation) is by far the most likely diagnosis. Standard practice is to initiate empirical anti-toxoplasma therapy (pyrimethamine + sulfadiazine + folinic acid) for 2 weeks and reassess; a clinical and radiological response confirms the diagnosis without biopsy. Primary CNS lymphoma (PCNSL) is the main differential; brain biopsy is reserved for non-responders. Toxo-seronegative patients with single lesion may need earlier biopsy.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.