Details: positivity for toxoplasma serology, lumbar puncture for CSF PCR, biopsy
CNS Toxoplasmosis is the most common cause of a focal brain mass in HIV patients. Basic differential diagnosis involves primary CNS Lymphoma. Both disorders occur at late-stage disease with a CD4+ count
The most common differentials are Toxoplasmosis and 1° CNS Lymphoma. The algorithm should depend on the local seroprevalence of toxoplasmosis (relatively high in Europe e.g.), the presence of toxo antibodies in Serum. CNS Toxoplasmosis is reactivated, so there will be antibodies in Serum in most cases, though very rarely CNS Toxoplasmosis can exist without serum antibodies. There is no radiological scan that can differentiate reliably between the diagnosis. CSF puncture should be performed if it is safe. In case of a positive serology, it may be ok to initiate treatment and evaluate the response, though 2 weeks is very short and most patients do not show a response within 2 weeks. In case a patient requires steroids due to the mass lesion, this is not possible however.
Brain biopsy is the gold standard and should be performed in all toxo negative cases, in cases in which toxo therapy has not induced remission, and in all cases of positive EBV PCR in CNS fluid! (primary CNS lymphoma is almost always EBV associated).
Recently had a case that turned out to be due to Nocardia... Initially treated as toxo and was improving, but reacted to bactrim, and hence switched to clindamycin. Eventually biopsied as he deteriorated following the switch...
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