Non-invasive versus invasive techniques for predicting idiopathic normal-pressure hydrocephalus in shunt-responsive patients

Abstract

The diagnosis of normal-pressure hydrocephalus (NPH) can be challenging, particularly distinguishing between shunt-responsive and non-responsive patients. Overlapping clinical symptoms with aging and neurodegenerative diseases such as Alzheimer's and Parkinson's may hinder its diagnosis. Thus, more effective diagnostic tools are necessary To compare non-invasive techniques, such as electroencephalography (EEG), transcranial Doppler (TCD), intracranial compliance (ICC) measurement, and optical coherence tomography (OCT), with invasive procedures, such as lumbar puncture (LP) and infusion tests (IT), in the prediction of shunt responsiveness in patients with idiopathic normal pressure hydrocephalus (iNPH). A systematic search of PubMed, Embase, and the Cochrane Library from 2013 to March 2023 identified studies that evaluated both invasive procedures (e.g., LP, IT) and non-invasive methods (e.g., EEG, TCD, ICC, OCT). Ten studies including 401 elderly patients with iNPH were analyzed. EEG biomarkers consistently differentiated responders, with three reproducible patterns: decreased frontal theta/delta power, increased temporal gamma power (sensitivity 83%, specificity 88%), and alpha rhythm normalization. Non-responders showed persistent slow delta waves in the frontal region and beta asymmetry. TCD revealed a 20% increase in the middle cerebral artery flow velocity after cerebrospinal fluid withdrawal in responders, correlating with motor improvement. OCT showed thinner ganglion cell layers in responders, while ICC suggested changes in brain compliance. Combined, these biomarkers may contribute to a more comprehensive predictive framework. While promising, non-invasive iNPH biomarkers remain insufficiently validated. No non-invasive test currently matches the reliability of invasive methods, which continue to represent the gold standard. Long-term data are lacking, and these tools should be considered as complementary rather than replacements for standard diagnostics.