A patient with advanced AIDS complicated by toxoplasmosis presents with altered mental status, seizures, and focal neurologic deficits. Which diagnostic study is most helpful?

• A. EEG
• B. MRI
• C. Lumbar puncture
• D. Toxoplasma gondii antibody titers

Answer: (B)

In AIDS patients with suspected toxoplasma encephalitis, imaging the brain is the most informative step because the infection creates focal inflammatory lesions that MRI can detect and characterize best. MRI has higher sensitivity than CT for identifying brain lesions, especially small or early ones, and it shows the typical pattern of multiple ring-enhancing lesions with surrounding edema, often in the basal ganglia and corticomedullary junction. This imaging pattern, in the right clinical setting, strongly supports toxoplasma encephalitis and helps distinguish it from other AIDS-related CNS problems such as CNS lymphoma, guiding management and, if needed, biopsy decisions. While lumbar puncture, toxoplasma antibody titers, and EEG can provide useful information in broader contexts, they are less definitive for diagnosing active toxoplasma encephalitis and carry limitations or risks in this scenario.