October 05, 2010

USMLE 2 Question 5

A 34 year old HIV positive patient develops a new-onset of confusion. A CT scan of the brain reveals multiple enhancing lesions.

The most likely diagnosis is:

a) HIV encephalitis
b) cryptococcus
c) PML
d) lymphoma
e) toxoplasmosis

The correct answer is E


The main differential diagnosis of focal brain lesions in HIV-infected patients is between CNS lymphoma and toxoplasmic encephalitis.

In T gondii-seropositive, HIV-infected patients with CD4 T-cell counts <100/┬ÁL, who are not receiving anti-T gondii prophylaxis, the presence of multiple enhancing lesions is strongly suggestive of toxoplasmic encephalitis.

In patients on prophylaxis, or those with a single brain lesion, the differential diagnosis includes CNS lymphoma, fungal abscess, mycobacterial or cytomegaloviral disease, or Kaposi sarcoma in addition to toxoplasmic encephalitis.

The absence of anti-T gondii IgG in serum strongly argues against the diagnosis of toxoplasmic encephalitis.

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