Normal Pressure Hydrocephalus: Likelihood Ratios

Introduction: None written.

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Prevalence

Population / Calculator	Prevalence	Comments / Study / Link
people > 65	0.41%	taken from a German town, confirmed by CT scan. Arch Neurol. 1995 Oct;52(10):1017-22. PMID: 7575219
Patients shunted for presumed NPH	29%	(i.e. percent responding to shunt) J Neurol Neurosurg Psychiatry. 1993 Mar;56(3):251-6. PMID: 8459240
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The likelihood ratios of findings for Normal Pressure Hydrocephalus are listed below. See the left navigation bar to change the display.

Good Positive and Negative Likelihood Ratios

Clinical and CT Diagnosis

3.4

0.5

'probable' NPH by all of the following criteria:

Clinical: 1) Predominance of gait disturbances; 2) Mental impairment ranging from not clinically present to moderate; 3) Absence of another disease which might explain the clinical symptoms.

CT: 1) Rounded frontal horns; 2) At least moderate ventriculomegaly (FHi 0 40 or higher); 3) Absence of moderate or severe cortical atrophy, and 4) Absence of moderate or severe white matter lucencies.

Study: J Neurol Neurosurg Psychiatry. 1993 Mar;56(3):251-6. PMID: 8459240

Good Positive Likelihood Ratio

External Lumbar Drainage

2.5

0.6

this involves placing a catheter in the spine and draining CSF over a longer time period (say, 72 hrs).

Another study reported sens = 97% , spec = 60%.

Study: Neurosurgery. 2005 Sep;57(3 Suppl):S17-28. PMID: 16160426

Poorly Diagnostic Findings

CSF Outflow Resistance

Another (lower class) study reported sens 100%, spec 92%.

Study: Neurosurgery. 2005 Sep;57(3 Suppl):S17-28. PMID: 16160426

CSF Removal

0.9

1.2

"tap test" - large-volume (>30 ml) removal of CSF by LP. 'Gold standard' was improvement after VP shunt placement.

Study: Neurosurgery. 2005 Sep;57(3 Suppl):S17-28. PMID: 16160426