When to perform a lumbar puncture in patients with suspected meningitis

In patients with suspected meningitis, a lumbar puncture should be performed as soon as possible, because cerebrospinal fluid (CSF) microscopy and culture are key to diagnosis and directed therapy of bacterial meningitis.

Most adults with suspected meningitis do not need imaging to determine the safety of lumbar puncture. A minority of patients have relative contraindications to lumbar puncture and a computed tomography (CT) scan may be indicated (eg patients with possible raised intracranial pressure, brain abscess or subarachnoid haemorrhage). If the CT scan is normal but the patient has signs of raised intracranial pressure, consider whether potential benefits of lumbar puncture outweigh potential harms – outcomes are improved when therapy can be directed and there is a very low risk of brain herniationCosterus 2018Glimaker 2018.

In children, CT scans are not routinely recommended in patients with possible raised intracranial pressure but may be used to investigate alternative diagnoses.

If lumbar puncture cannot be performed urgently in patients with suspected meningitis, review and reassess the patient regularly, and perform lumbar puncture when feasible or when contraindications resolve. If clinical suspicion of bacterial meningitis is high, start antibiotics while waiting for lumbar puncture or scans to be performed; see Antibiotic timing in patients with suspected meningitis.