Question

A patient with HIV and a CD4 count <40 cells/mm³ presents with a ring-enhancing lesion in the brain on contrast imaging. What is the most likely diagnosis?

• A. Lymphoma
• B. Toxoplasma
• C. Tuberculosis
• D. Progressive multifocal leukoencephalopathy (PML)

Hint:

CD4 <100 plus ring enhancement in HIV → think the commonest opportunistic CNS infection first.

Answer 1

The Correct Option is B

Step 1: Identify the clinical setting.
This is an HIV patient with a CD4 count <40 cells/mm³, i.e. profound immunosuppression (AIDS-defining range). In this group, opportunistic CNS infections become highly likely.

Step 2: Apply the imaging clue.
A contrast ring-enhancing lesion in the brain in advanced HIV most classically points to cerebral toxoplasmosis (reactivation of Toxoplasma gondii). It typically produces multiple ring-enhancing lesions with a predilection for the basal ganglia and grey-white junction, with surrounding oedema.

Step 3: Eliminate the other options.
• Primary CNS lymphoma tends to be a single, more solid/homogeneously enhancing periventricular lesion (though it can ring-enhance, it is usually solitary and shows restricted diffusion); thallium-SPECT/PET uptake helps distinguish it.
• Tuberculoma is possible but less characteristic at this very low CD4 count as the lead answer.
• PML classically causes non-enhancing, asymmetric white-matter demyelination (JC virus) and does not produce ring enhancement.

Step 4: Conclusion.
Multiple ring-enhancing lesions in an HIV patient with CD4 <40 are most likely toxoplasmosis; empirical anti-toxoplasma therapy with response on follow-up imaging is standard. Key fact: Toxoplasmosis is the commonest cause of ring-enhancing brain lesions in advanced HIV/AIDS.