Until the 1980s, primary central nervous systemlymphoma (PCNSL) was a rare disease. PCNSL has increased dramatically in association with AIDS. PCNSL accounts for approximately 0.6% of initial AIDS diagnoses and is the second most frequent central nervous system (CNS) mass lesion in adults with AIDS. As with other AIDS-related lymphomas, these are usually aggressive B-cell neoplasms, either diffuse large cell or diffuse immunoblastic non-Hodgkin lymphoma. Unlike AIDS-related systemic lymphomas, in which 30% to 50% of tumors are associated with Epstein-Barr virus (EBV), AIDS-related PCNSL has been reported to have a 100% association with EBV. This percentage indicates a pathogenetic role for EBV in this disease. These patients usually have evidence of far-advanced AIDS, are severely debilitated, and present with focal neurologic symptoms such as seizures, changes in mental status, and paralysis.
Computed tomographic scans show contrast-enhancing mass lesions that may not always be distinguished from other CNS diseases, such as toxoplasmosis, that occur in AIDS patients. Magnetic resonance imaging studies using gadolinium contrast may be a more useful initial diagnostic tool in differentiating lymphoma from cerebral toxoplasmosis or progressive multifocal leukoencephalopathy. Lymphoma tends to present with large lesions, which are enhanced by gadolinium. In cerebral toxoplasmosis, ring enhancement is very common, lesions tend to be smaller, and multiple lesions are seen.[4,5,6] Use of positron emission scanning has demonstrated an improved ability to distinguish PCNSL from toxoplasmosis.[7,8]
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PSNCL has an increased uptake while toxoplasmosis lesions are metabolically inactive. Antibodies against toxoplasmosis may also be very useful because the vast majority of cerebral toxoplasmosis occur as a consequence of reactivity of a previous infection. If the IgG titer is less than 1:4, the disease is unlikely to be toxoplasmotic. A lumbar puncture may be useful to detect as many as 23% of patients with malignant cells in their cerebrospinal fluid (CSF). Evaluating the CSF for EBV DNA may be a useful lymphoma-specific tool since EBV is present in all patients with PCNSL. Despite all of these evaluations, however, the majority of patients with PCNSL require a pathologic diagnosis.[9,10,11] Diagnosis is made by biopsy. Sometimes, a biopsy is attempted only after failure of antibiotics for toxoplasmosis, which will produce clinical and radiographic improvement within 1 to 3 weeks in patients with cerebral toxoplasmosis. PCNSL is often identified as a terminal manifestation of AIDS or on postmortem examination.