Lumbar Puncture

Question 1

Describe the anatomical position that is used in guiding a lumbar puncture?

Answer 1

L3-L4 as this is the area of the cauda equina therefore there is no risk of spinal cord damage (spinal cord terminates at L1/L2.

Question 2

Describe the position in which a patient should be if you need to perform a lumbar puncture on them?

Answer 2

Lying on their left side with their back exactly vertical, aligned with the edge of the bed, with their spine fully flexed - knees up to chin.

Or sitting up right with there back flexed forward.

Question 3

What are the potential complications of a lumbar puncture?

Answer 3

Post-LP headache.*

Infection.

Bleeding (approximately 2%).

Cerebral herniation (rare but potentially fatal) aka coning therefore imaging should be done 1st if you are worried about raised intracranial pressure.

*Headache is the most common complication of LP. It lasts for 2-8 days and occurs in around 40% of patients. It is caused by low CSF pressure due to fluid leakage through the hole (so-called ‘dural tap’).

Question 4

What are the contraindications to lumbar puncture?

Answer 4

1. Signs suggested of raised intracranial pressure
2. Shock.
3. Extensive or spreading purpura.
4. Convulsions until stabilised.
5. Coagulation abnormalities:
6. Superficial infection at the LP site.
7. Respiratory insufficiency: LP has a high rate of triggering respiratory failure in those with insufficiency

Question 5

What are the signs of raised intracranial pressure?

Answer 5

• Fluctuating/reduced level of consciousness GCS less than 9 or a drop of 3
• Age-relative bradycardia and hypertension.
• Focal neurological signs.
• Abnormal posture or posturing.
• Unequal, dilated or poorly responsive pupils.
• Papilloedema
• Bulging fontanelle

Question 6

What are the indications for a lumbar puncture?

Answer 6

Investigation:

• Suspected meningitis.
• Intercranial bleed/SAH if CT or MRI do not confirm the diagnosis

Treatment:

• To administer intrathecal medication
• To treat normal pressure hydrocephalus
• Benign intercranial hypertension

Question 7

What is CSF xanthocromia and what is its clinical significance?

Answer 7

CSF xanthochromia is the yellow discoloration indicating the presence of bilirubin in the cerebrospinal fluid (CSF).

It is clinically significant as it indicates that there has been a SAH or other intracranial bleed. It is present from 12hours after a bleed and is still up to 2 weeks after an event.

Conversely CT scanning will show no sign of a bleed in 5% of patients at 24hrs post event and upto 50% after 1 week.

Question 8

What are the CSF findings associated with multiple sclerosis?

Answer 8

Cerebral spinal fluid studies can confirm demyelinating disease of the nervous system.

CSF studies can show:

• an increase in immunoglobulin concentrations in more than 90% of patients with MS.
• an IgG index (a comparison between IgG levels in the CSF and in the serum) which is elevated in many MS patients.
• identification of Oligoclonal Immunoglobulin Bands consistent with MS via electrophoresis of CSF.