Neoplastic meningitis

Neoplastic meningitis is recognized clinically in 4% to 7% of patients with extraneural cancer, but it remains dramatically under-diagnosed. The frequency of neoplastic meningitis is increasing because of heightened clinical suspicion, improved neuroimaging techniques, and longer survival in patients with extraneural cancer Longer survival allows residual tumor cells within central nervous system sanctuary sites time to become symptomatic. Affected patients may present with cerebral, cranial nerve, or spinal signs and symptoms, depending on the specific sites of central nervous system (CNS) involvement. Magnetic Resonance Imaging (MRI) seems to be sensitive for detecting metastatic deposits along the neuraxis. However, metastases at a microscopic level are below the resolution of MRI scanning. As a result, the standard diagnostic test for neoplastic meningitis remains the cytologic identification of malignant cells in cerebrospinal fluid (CSF). Although CSF cytology is useful, malignant cells are not detected in as many as one third of patients who have compelling clinical or radiographic evidence of neoplastic meningitis. Novel assays are being tested that may enhance the early identification of malignant cells in CSF. Currently, the diagnosis occurs generally after the onset of neurologic manifestations and heralds a rapidly fatal course for most patients. By the time symptoms appear, most tumors have disseminated widely within the CNS, due to cortical irritation, compression of nervous system structures, or obstruction of CSF flow. At this stage surgery, cranial irradiation, and chemotherapy are rarely, if ever, curative. The goals of treatment are to improve or to stabilize the neurologic status of patients and to prolong survival. A major problem in treating neoplastic meningitis is that the entire neuraxis must be treated. If only symptomatic areas are treated, reseeding of the neuraxis with tumor cells will occur. Therefore, intrathecal chemotherapy remains a mainstay of therapy. Currently, four therapeutic agents are available for intrathecal treatment: methotrexate, ara-C, sustained-release ara-C (DepoCyt; Chiron Therapeutics, San Francisco, CA), and thiotepa. Unfortunately, intrathecal chemotherapy does not treat bulky disease in the subarachnoid space, and often is slow to stabilize progressive neurologic deficits. For these reasons, radiation therapy to sites of symptomatic disease and sites of bulky disease on imaging studies is recommended. High dose intravenous methotrexate may be as effective as intrathecal methotrexate. Alternative approaches (which offer less toxicity, enhanced therapeutic effect, and prolonged survival) are being investigated.