Lumbar Puncture

Question 1

How would you explain the procedure?

What is the main benefit to the patient of doing an LP?

When is it used therapeutically?

Answer 1

A ‘spinal tap’ involves using a needle to obtain a sample of the fluid surrounding the spinal cord (and the brain)

Aids diagnosis

For raised ICP

Question 2

Risks:

Common risks?

What may happen after?

Answer 2

Back pain - shooting down the legs - hitting a nerve
Localised bleeding

Persistent headache
Infection
Lower limb weakness

Question 3

Indications - when is it used to aid diagnosis? - 3

When is a spinal epidural used?

Answer 3

Infection - meningitis/encephalitis
SAH
MS - aids diagnosis - monoclonal bands

Pain relief - during labour - epidural
Anaesthesia (lower limb surgery) - the patient is awake

Question 4

Cautions and contraindications:

Imaging is not necessarily needed unless you suspect raised ICP. What signs may suggest this?

Bleeding risk - Low platelet count and anticoagulation

Answer 4

Focal neurological signs
Papilloedema
Continuous/uncontrolled seizures
Reduced GCS

Question 5

Technique:

2 positions that can be used?

Technique used?

Answer 5

Lying position or sitting positions

Ideally an US guided technique

Question 6

Beside assessment:

Appearance:

• What should it normally look like?
• What suggests meningitis?
• What does blood in the CSF indicate? - 2

Opening pressure:

• What is the normal opening pressure?
• What may cause it to the raised?

Answer 6

SAH/Traumatic tap

Clear (gin-coloured)

Cloudy/purulent

8-20 cm

Inflammation - meningitis
Haemorrhage
Raised ICP

Question 7

What 3 components of CSF are used for diagnosis?

What 3 methods are used to identify the pathogen?

Answer 7

Cell count - RBC, WBC
Glucose
Protein

Gram stain + Culture - MC+S
PCR

Question 8

CSF analysis:

Cell count:
- RBC - raised in 2 situations?

WBC:
- What is seen in bacterial meningitis?
What is seen in viral/TB meningitis/encephalitis (& inflammatory conditions and malignancy)?

NOTE - IT CAN BE A MIXED PICTURE

Protein - What causes RAISED protein? - 2
What sort of protein is seen in MS?

Glucose:

• What does this need to be compared to?
• A drop of more than 50% suggests that there is some pathology.

What is the main cause for low glucose?

Answer 8

SAH/Traumatic tap

Raised neutrophils - B meningitis

Raised lymphocytes

====
Infection (TB>bacterial>viral) meningitis
Inflammatory conditions

Oligoclonal bands - MS

====
Serum glucose - usually 60-80% of serum glucose

Infection - Meningitis - all types

Question 9

Diagnosing Infection:

Gram stain for diagnosis:

Gram positive:
- Why are these bacteria dark purple?
Example - Strep Pneumoniae:
- Appearance on gram stain?

Gram negative:
- Why are these bacteria pink?

Example - Neisseria Meningitides - They are cocci - what sort of chain are they in?

Culture - What should you make sure you do this before? How long does it take?

What can be used to identify bacteria (N. meningitidis/Strep pneumoniae) and viruses (TB)

Answer 9

Peptidoglycan wall retains crystal violent STAIN

It is therefore dark PURPLE

Lack of peptidoglycan in cell wall
Crystal violet not retained
Counter stained with safarin stain - allows visualisation
Therefore it is pink

Diplococci - in pairs

======
Prior to administering ABs - kills bacteria and you can’t identify type of bacteria

24-72 hrs - start empirical ABs until sensitivity known

PCR - polymerase chain reaction