Seen at all ages, but peak after the 5th decade. Puzzling is that the incidence seems to be rising in immunocompetent patients. Likewise, it is rare for patients who present with PCL to show systemic disease. There are no reported cases of familial PCL in immunocompetent patients but a number of factors predispose patients to develop lymphoma. Organ transplant recipients have increased risk.
Risk increases with duration and extent of suppression.
SLE, Sjogren's, Rheumatoid arthritis. Primary CNS lymphomas are in every way similar to their systemic counteparts derived from B cells. Primary CNS T-cell lymphomas are very rare. The cell of origin remains unclear although transformed lymphocytes, microglia, and histiocytes have been implicated. Multifocal or bilateral lesions are not uncommon, especially in AIDS patients.