Lumbar puncture

Contraindications

• Increased intracranial pressure, with focal neurological deficits, new seizures, or papilledema
• Infection at the procedure site
• Coagulopathy
  • Platelets <30
  • INR >1.6
  • Hemophilia
  • Anticoagulation

Procedure

• Position appropriately: lateral decubitus or sitting and leaning over a table
• Landmark using posterior superior iliac crests (PSIS) (marks L4)
  • Can go above (L4/L5 space) or below (L3/L4 space)
• Inset spinal needle in the midline
• Measure opening pressure

Investigations

• Consider INR/PTT if concern about coagulopathy
• Consider platelet count (should be >100)
• Consider CT head

Complications

• Local pain
• Post-LP headache, better when supine
  • Treat with caffeine, fluids, and acetaminophen
• Brief radicular pain
• Rare:
  • Spinal epidural hematoma
  • Bacterial meningitis or spinal abscess
  • Cerebral herniation

Interpretation

Etiology	Gram stain	Cell count	CSF glucose	CSF protein
Bacterial meningitis	Positive in 60-80%	Elevated >1000 neutrophils	Reduced <0.4 CSF:serum	Elevated >1g/L
Viral meningitis	Negative	Moderate elevation <100 lymphocytes	Normal or mildly reduced	Normal or mildly elevated
Fungal or tuberculous meningitis	Negative, except for cryptococcus on India ink or TB on acid-fast	Moderate elevation, usually lymphocytes	Often very low	Elevated

• Correction for a bloody tap is 1 excess WBC for every 700 RBCs
• Lymphocytosis may be seen in bacterial meningitis if Listeria infection or prior antibiotics
• Xanthochromia suggests subarachnoid hemorrhage

CSF After Antibiotics

• Glucose increases first, then protein, and both are often normalized within 12 hours
• WBC normalizes last, and can still be useful even the following day

Further Reading

• Straus S, et al. How Do I Perform a Lumbar Puncture and Analyze the Results to Diagnose Bacterial Meningitis? JAMA. 2006;296(16):2012-2022.