Indications Diagnostic indications * Suspected central nervous system (CNS) infection (acute bacterial meningitis, viral meningitis, encephalitis, subacute or chronic meningitis) Suspected multiple sclerosis or autoimmune encephalitis (eg, anti-NMDAR encephalitis) Suspected spontaneous subarachnoid hemorrhage not diagnosed on neuroimaging or if immediate neuroimaging is not available Suspected idiopathic intracranial hypertension Suspected intracranial hypotension Other CNS conditions, including Guillain-Barré syndrome, leptomeningeal metastases (carcinomatous meningitis), genetic metabolic encephalopathies To give a radiopaque contrast agent for myelography * Decide in advance what information you need from the lumbar puncture and what tests you need to order.