Patients with non-Hodgkin’s lymphoma often have neurological complications. These include not only metastases, but also infectious, toxic-metabolic, cerebrovascular, paraneoplastic, and treatment related complications. Infections of the CNS related to disease induced immunosuppression occur with increased frequency; toxoplasmosis, fungal meningitis, herpes zoster, and papova virus infection leading to progressive multifocal leukoencephalopathy are among the most common. Metabolic encephalopathy from organ failure, sepsis, and drug induced encephalopathy commonly produce confusion, lethargy, seizures, and occasionally coma. Strokes from non-bacterial thrombotic endocarditis, disseminated intravascular coagulation, and venous sinus occlusion can produce lateralising or global CNS symptoms. Paraneoplastic syndromes seen in non-Hodgkin’s lymphoma include motor neuronopathy and necrotising myelopathy. Treatment induced neurotoxicities include vincristine neuropathy, ifosfamide or cytarabine encephalopathy, radiation myelopathy, or radiation related cognitive impairment. A comprehensive discussion of these many entities is beyond the scope of this editorial, but can be found in several recent monographs.1 2 The CNS may also be directly involved by lymphoma, either metastatic or primary. Lymphoma of the CNS is often a major diagnostic challenge for the neurologist and will be the focus of this discussion.

Non-Hodgkin’s lymphoma is a collection of diseases involving malignant transformation of usually B lymphocytes. Typically, the disease presents with adenopathy involving the major lymph node chains throughout the body. Other organs can become involved in later stages of the disease, usually due to haematogenous metastases which arise from nodal sites or bone marrow involvement. Occasionally, the disease can arise in a non-lymphoid organ such as skin or the gastrointestinal tract, but lymphocytes are an important component of the normal structure of these organs. The CNS contains no lymph nodes or lymphatics. Metastatic lymphoma spreads to the CNS usually as a consequence of haematogenous dissemination from widespread systemic disease. Given the absence of a lymphatic system in the CNS, it would …