Treatment of AIDS-Related Primary Central Nervous System Lymphoma

As with other AIDS-related lymphomas, primary central nervous system (CNS) lymphoma (PCNSL) is an aggressive B-cell neoplasm, either diffuse large B-cell or diffuse immunoblastic non-Hodgkin lymphoma (a subtype of diffuse large B-cell lymphoma). AIDS-related PCNSL has been reported to have a 100% association with Epstein-Barr virus (EBV).[1] These patients usually have evidence of low CD4-positive T lymphocyte counts, high HIV viral load, severe debilitation, and focal neurological 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 patients with AIDS.[2] 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.[3-5] Use of positron emission scanning has demonstrated an improved ability to distinguish PCNSL from toxoplasmosis.[6,7] PCNSL has an increased uptake while toxoplasmosis lesions are metabolically inactive. Antibodies against toxoplasmosis may also be very useful because most cerebral toxoplasmosis occurs as a consequence of reactivity of a previous infection. If the immunoglobulin G 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 because EBV is present in all patients with PCNSL. Despite the many evaluations, however, most patients with PCNSL require a pathological diagnosis.[8-10] 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.[11]

Radiation therapy alone has usually been used in this group of patients. With doses in the range of 35 Gy to 40 Gy, median duration of survival has been only 72 to 119 days.[2,12,13] Survival is longer in younger patients with better performance status and the absence of opportunistic infection.[14] In the highly active antiretroviral therapy (HAART) era, a median survival of 18 months has been seen with radiation therapy alone.[15] An anecdotal report using HAART and high-dose methotrexate for patients with AIDS-related PCNSL showed a median survival that had not been reached with a median follow-up of 27 months.[16] Most patients respond to treatment by showing partial improvement in neurological symptoms. Autopsies have revealed that these patients die of opportunistic infections as well as tumor progression. Treatment of these patients is also complicated by other AIDS-related CNS infections, including subacute AIDS encephalitis, cytomegalovirus encephalitis, and toxoplasmosis encephalitis. Spontaneous remissions have been reported after HAART.[17]