REVIEW  IDIOPATHIC NORMAL PRESSURE HYDROCEPHALUS REVISITED: THE ROLE OF INTERDISCIPLINARITY Open access

Journal of Neurosurgical Sciences 2025 February;69(1):46-63

DOI: 10.23736/S0390-5616.24.06368-9

Copyright © 2024 THE AUTHORS

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Standardizing the large-volume “tap test” for evaluating idiopathic normal pressure hydrocephalus: a systematic review

Brent BLUETT ¹ ✉, Lealani M. ACOSTA ², Elissa ASH ^{3, 4}, Bastiaan R. BLOEM ⁵, Alberto J. ESPAY ⁶, Amtul FARHEEN ^{7, 8}, Alfonso FASANO ^{9, 10, 11, 12, 13}, Alissa HIGINBOTHAM ¹⁴, Joachim K. KRAUSS ¹⁵, Anthony E. LANG ^{9, 10}, Giovanni MOSTILE ^{16, 17}, Iciar AVILES-OLMOS ¹⁸, Andrea QUATTRONE ^{19, 20}, Philip W. TIPTON ²¹, David F. TANG-WAI ^{9, 11} on behalf of the International Parkinson and Movement Disorders Society Normal Pressure Hydrocephalus (MDS-NPH) Study Group

¹ Central California Movement Disorders, Santa Barbara, CA, USA; ² Department of Neurology, Vanderbilt University Medical Center, Nashville, TN, USA; ³ Department of Neurology, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel; ⁴ Faculty of Medicine, University of Tel Aviv, Tel Aviv, Israel; ⁵ Department of Neurology, Center of Expertise for Parkinson & Movement Disorders, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, the Netherlands; ⁶ Department of Neurology, James J. and Joan A. Gardner Family Center for Parkinson’s Disease and Movement Disorders, University of Cincinnati, Cincinnati, OH, USA; ⁷ Department of Neurology, G.V. (Sonny) Montgomery VA Medical Center, Jackson, MS, USA; ⁸ Department of Neurology, University of Mississippi, Oxford, MS, USA; ⁹ Division of Neurology, Department of Medicine, University of Toronto, Toronto, ON, Canada; ¹⁰ Edmond J. Safra Program in Parkinson’s Disease, Rossy PSP Center, University of Toronto, Toronto, ON, Canada; ¹¹ The Howard Cohen Normal Pressure Hydrocephalus Program, Krembil Brain Institute (Toronto Western Hospital), University Health Network, Toronto, ON, Canada; ¹² Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Milan, Italy; ¹³ IRCCS Humanitas Research Hospital, Rozzano, Milan, Italy; ¹⁴ Department of Neurology, University of Virginia School of Medicine, Charlottesville, VA, USA; ¹⁵ Department of Neurosurgery, Hannover Medical School, Hannover, Germany; ¹⁶ Department of Medical, G.F. Ingrassia Surgical Sciences and Advanced Technologies, University of Catania, Catania, Italy; ¹⁷ Oasi Research Institute - IRCCS, Troina, Enna, Italy; ¹⁸ Department of Neurology, Clinical University of Navarra, Pamplona, Spain; ¹⁹ Neuroscience Research Center, Magna Graecia University, Catanzaro, Italy; ²⁰ Department of Medical and Surgical Sciences, Institute of Neurology, Magna Graecia University, Catanzaro, Italy; ²¹ Department of Neurology, Mayo Clinic, Jacksonville, FL, USA

INTRODUCTION: Idiopathic normal pressure hydrocephalus (iNPH) is characterized by the clinical triad of gait, cognitive, and urinary dysfunction associated with ventriculomegaly on neuroimaging. Clinical evaluation before and after CSF removal via large volume lumbar puncture (the “tap test”) is used to determine a patient’s potential to benefit from shunt placement. Although clinical guidelines for iNPH exist, a standardized protocol detailing the procedural methodology of the tap test is lacking.
EVIDENCE ACQUISITION: Using PRISMA guidelines, a systematic review of PubMed and Embase identifying studies of the tap test in iNPH was performed, centered on four clinical questions (volume of CSF to remove, type of needle for lumbar puncture, which clinical assessments to utilize, and timing of assessments). A modified Delphi approach was then applied to develop a consensus standardized tap test protocol for the evaluation of idiopathic normal pressure hydrocephalus.
EVIDENCE SYNTHESIS: Two hundred twenty-two full-text articles encompassing a total of 80,322 participants with iNPH met eligibility and were reviewed. Variations in the tap test protocol resulted in minimal concordance among studies. A standardized protocol of the tap test was iteratively developed over a two-year period by members of the International Parkinson and Movement Disorders Society Normal Pressure Hydrocephalus Study Group until expert consensus was reached.
CONCLUSIONS: The literature shows significant variability in the procedural methodology of the tap test. The proposed protocol was subsequently developed to standardize clinical management, improve patient outcomes, and better align future research in idiopathic normal pressure hydrocephalus.

KEY WORDS: Hydrocephalus, normal pressure; Spinal puncture; Clinical protocols