Lumbar puncture
From IDWiki
Contraindications
- Increased intracranial pressure, with focal neurological deficits, new seizures, or papilledema (CT head first; see Investigations, below)
- Infection at the procedure site
- Coagulopathy
- Platelets <30-40
- INR ≥1.4-1.6
- Hemophilia
- Anticoagulation
- Within 4 hours of prophylactic low molecular weight heparin (LMWH)
- Within 24 hours of therapeutic LMWH
- Within 7 days of clopidogrel (but no delay for aspirin)
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 if focal neurological signs, papilledema, GCS ≤12
- IDSA: immunocompromised, history of CNS disease (including stroke and mass lesion), or new, uncontrolled, or continuous seizures
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 stain | 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
- Hypoglycorrhachia refers to low CSF glucose
Interpretation 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
Opening Pressure
- Usual range is 5 to 20 cm H2O
- See causes of increased intracranial pressure
Protein
- May be increased by disruption of the blood-brain barrier (most commonly), intracranial synthesis of IgG, or impaired CSF resorption of proteins by the arachnoid villi
- Highly suggestive of CNS disease
Correction for Traumatic Tap
- If increased RBCs are seen, may need to adjust
- Allow 1 WBC for every 700-1000 RBCs
- Allow 0.01 mg/mL protein for every 1000 RBCs
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.
