Instrumented gait analysis for an objective pre-/postassessment of tap test in normal pressure hydrocephalus.

OBJECTIVE To present an objective method to evaluate gait improvements after a tap test in idiopathic normal pressure hydrocephalus (INPH). DESIGN Retrospective analysis of gait data. SETTING Public tertiary care center, day hospital. The gait analysis was performed before and 2 to 4 hours after the tap test. PARTICIPANTS Participants included patients with INPH (n=60) and age- and sex-matched controls (n=50; used to obtain reference intervals). From an initial referred sample of 79 patients (N=79), we excluded those unable to walk without walking aids (n=9) and those with incomplete (pre-/posttap test) gait data (n=10). Thirteen out of 60 patients were shunted and then reappraised after 6 months. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Mahalanobis distance from controls, before and after the tap test. Eleven gait parameters were combined in a single quantitative score. Walking velocity was also evaluated because it is frequently used in tap test assessment. RESULTS Patients were classified into 2 groups: tap test responders (n=22, 9 of them were shunted) and not suitable for shunt (n=38, 4 of them were shunted). In the tap test responders group, 9 out of 9 patients improved after shunt. In the not suitable for shunt group, 3 out of 4 patients did not improve. Gait velocity increased after the tap test in 53% of responders and in 37% of patients not suitable for shunt. CONCLUSIONS The new method is applicable to clinical practice and allows for selecting tap test responders in an objective way, quantifying the improvements. Our results suggest that gait velocity alone is not sufficient to reliably assess tap test effects.