Investigations

Lumbar puncture ^a  

Why?

• One in seven patients requiring an urgent lumbar puncture has an intracranial lesion on CT scan (15%: 95% CI: 8.6% to 22%) ^a and one in forty has a contraindication. (2.7%: 95% CI: 0.0% to 5.7%) ^a

Papilloedema , focal neurological signs, and altered mentation make an intracranial lesion more likely.

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
urgent need for lumbar puncture a (pre-test probability: 15%)	intracranial mass (CT head)	papilloedema	11 (1.1 to 120)	67%	0.89 (0.75 to 1.1)	14%
		focal neurological signs	4.3 (1.9 to 10)	44%	0.64 (0.38 to 1.0)	10%
		altered mentation	2.2 (1.5 to 3.2)	28%	0.36 (0.15 to 0.90)	6%
		1 or more abnormality present	1.6 (1.2 to 1.9)	22%	0.0 (0.0 to 0.6)	0%
		physician's prediction of a new lesion	9.1 (2.4 to 34)	62%	0.63 (0.40 to 1.0)	10%

 

A physician's prediction of no contraindication to lumbar puncture makes a contraindication less likely but does not clearly rule one out.

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
urgent need for lumbar puncture a (pre-test probability: 2.7%)	contraindication (CT brain)	physician's prediction of a contraindication	19 (4.8 to 43)	34%	0.0 (0.0 to 0.7)	0%

Note:

• None of the following features were found to predict intracranial lesions ^a
  • HIV positive or HIV risk factors
  • immunosuppressed
  • malignant neoplasm
  • head trauma within previous 72 hours
  • known CNS mass
  • seizures within previous 72 hours