OBJECTIVES: To evaluate the sustained effects of the cerebrospinal fluid (CSF) tap test (TT) on gait parameters over one month in patients with idiopathic normal pressure hydrocephalus (iNPH). METHODS: A retrospective study was conducted on 150 patients with iNPH from two university hospitals who underwent CSF TT and quantitative gait analysis. Gait parameters, including walking speed (WS) and stride length (SL), were measured before, within 24 h after, and one month after the CSF TT. The primary outcome was the proportion of patients showing a 20% or greater improvement. We used stratified logistic regression analysis to analyze which demographic variables were associated with sustained response one month after TT and nested linear mixed model to evaluate changes in gait parameters. RESULTS: Within 24 h after the CSF TT, 42.67% of patients improved in WS, and 30.67% in SL. One month later, 43.33% of the patients maintained improved WS, and 31.33% maintained improved SL. Stratified logistic regression analysis revealed that lower pre-CSF TT WS or SL were significant predictors of long-term gait improvement. Nested linear mixed model analysis revealed significant improvements in WS (10.815 cm/s immediately post-TT
9.408 cm/s one month post-TT) and SL (9.506 cm immediately post-TT
8.637 cm one month post-TT). CONCLUSION: This study demonstrated that the CSF TT can result in sustained improvements in gait parameters in iNPH patients, suggesting that repeated evaluations over time may aid in determining the appropriate treatment strategies for patients in whom surgical treatment plans are not immediately determined after the CSF TT.