Input the walking response, cognitive change, and underlying status to predict the likelihood of permanent shunt success.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Evaluating elderly patients with the Hakim-Adams triad (Wait, Wobbly, Wacky) for Idiopathic Normal Pressure Hydrocephalus (iNPH).
Selecting surgical candidates for permanent Ventriculoperitoneal (VP) shunting.
Section 2
Literature
Development
The "Tap Test" or Large Volume Lumbar Puncture (LVLP) was standardized to prevent the massive over-shunting of the 1980s. When iNPH was discovered, surgeons started shunting every elderly patient with dementia and large ventricles, resulting in high complication rates and no cure for Alzheimer's. Removing 40-50cc of CSF allows a temporary "preview" of shunt efficacy.
Section 3
Pearls/Pitfalls
Gait First, Cognition Last
The pathophysiology of iNPH involves the enlarged ventricles stretching the long trans-cerebral motor tracts descending to the legs. Therefore, GAIT improvement is the most sensitive and earliest responder to a tap test. Cognitive improvement happens slowly (if at all), and incontinence is unpredictable. Base your surgical decision on objective gait metrics (e.g. 10-meter walk time).
Section 4
Evidence Appraisal
Primary Reference
Normal pressure hydrocephalus. Predictive value of the cerebrospinal fluid tap-test
Wikkelsø C et al. • Acta Neurol Scand. 1986;73(6):566-73
