Suspected meningitis. If you suspect bacterial meningitis take blood cultures and start antibiotic therapy immediately, before lumbar puncture (Chapter 68 ).

Suspected encephalitis. If you suspect viral encephalitis start aciclovir immediately, before lumbar puncture(Chapter 69).

Suspected subarachnoid haemorrhage. Wait 12h from onset of headache before performing lumbar puncture(Chapter 67).

Suspected idiopathic intracranial hypertension. Other causes of raised CSF pressure must be excluded first(Chapter 72).

• Suspected Guillain-Barré syndrome (Chapter 71).
• Suspected new acute presentation of multiple sclerosis.

Contraindications^*

• Reduced level of consciousness
• Papilloedema
• Focal neurological signs
• Recent seizure
• Bleeding disorder (including platelet count <50×10⁹/l, INR >1.5, receiving oral anticoagulant or anticoagulant-dose heparin)
• Local skin infection
• Anatomical abnormality, for example myelomeningocoele

Complications

• Post-lumbar puncture headache (reportedly less frequent with atraumatic needle)
• Cerebral herniation (can occur in setting of internal CSF pressure gradient)
• Nerve root injury causing radicular pain or sensory disturbance
• Bleeding causing spinal cord injury
• Meningitis due to introduction of infection