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Normal Pressure Hydrocephalus: Sensitivity and Specificity

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 sensitivity and specificity of findings for Normal Pressure Hydrocephalus are listed below. See the left navigation bar to change the display.

Pre-Test Probability (Prevalence): %.	Post-Test Probability (Predictive Value): %.	Switch to display mode.
Note that calculating probabilities from more than one** finding is inherently inaccurate because findings are not independent. (For example, using two positive findings that share a common pathogenesis is likely to overestimate the true probability.)

Negative Findings
Finding	Result	Sensitivity	Specificity
[ + ] CSF Removal	+ 0 -	62%	33%
"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

Poorly Diagnostic Findings
Finding	Result	Sensitivity	Specificity
[ + ] Clinical and CT Diagnosis	+ 0 -	54%	84%
'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
[ + ] External Lumbar Drainage	+ 0 -	50%	80%
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
[ + ] CSF Outflow Resistance	+ 0 -	58%	44%
Another (lower class) study reported sens 100%, spec 92%. Study: Neurosurgery. 2005 Sep;57(3 Suppl):S17-28. PMID: 16160426