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

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.