Keeping an open mind about meningitis: a case report of carcinomatous meningitis.

Carcinomatous meningitis is defined as leptomeningeal infiltration by malignant cells. A case of carcinomatous meningitis, originally diagnosed as viral meningitis, is presented here to highlight the importance of maintaining a broad differential diagnosis in patients with evidence of meningeal irritation. Clinical and laboratory clues that suggest a diagnosis of carcinomatous meningitis in a patient with meningeal irritation include the presence and type of underlying malignancy (more common with breast cancer, lung cancer, and melanoma), absence of fever, presence of radicular pain, evidence of both cranial and spinal involvement, consistent cerebrospinal fluid (CSF) findings (increased opening pressure, elevated protein concentration, decreased glucose, increased white cell count), and supportive neuroimaging. Diagnosis is based on positive CSF cytology results, which may require multiple lumbar puncture procedures to obtain. For patients with a known primary malignancy who present to the emergency department with symptoms and/or signs of meningeal irritation, carcinomatous meningitis should be included in the differential diagnosis.