Alteration of Postural Stability after Cerebrospinal Fluid Tap Test in Patients with Idiopathic Normal Pressure Hydrocephalus

Abstract

Abstract Background In patients with idiopathic normal pressure hydrocephalus (iNPH), the characteristics of balance disturbance are less understood than those of gait. We examined the changes in postural stability after the cerebrospinal fluid tap test (CSFTT) during quiet standing. Furthermore, we explored the relationship between frontal lobe function and the amount of spontaneous body sway. Methods All patients with iNPH underwent CSFTT and were evaluated using a frontal assessment battery (FAB) and center of pressure (COP) using a force plate during quiet standing before and after CSFTT. After COP measurement, we calculated COP parameters using time and frequency domain analysis. We determined whether there were alterations of COP parameters before and after CSFTT and the relationship between FAB and COP parameters using SPSS. Results In total, 72 patients with iNPH were recruited, and 56 patients who positively responded to CSFTT were finally included. Following CSFTT, there were significantly improved COP parameters using time domain analysis (velocity of COP, vCOP, p = 0.002; root-mean-square of COP, p = 0.032; turn index, p = 0.017; torque, p = 0.003; base of support, BOS, p = 0.014) compared to before CSFTT. In COP parameters using frequency domain analysis after CSFTT, we observed decreased power spectral density (PSD) values in the anteroposterior (peak value, p = 0.049; average value, p = 0.030) and mediolateral (peak value, p = 0.003; average value, p = 0.028) directions at low-frequency oscillation, below 0.5 Hz. In addition, FAB scores were negatively correlated with the vCOP (r = − 0.359, p = 0.007), BOS (r = − 0.302, p = 0.025), and the peak PSD value (r = − 0.464, p = 0.002) and average PSD value (r = − 0.424, p = 0.004) in anteroposterior direction for iNPH patients, respectively. Conclusions In patients with iNPH who responded to CSFTT, spontaneous body sway during quiet standing improved after CSFTT. The increased spontaneous sway is associated with impaired frontal lobe function, which may be linked to postural control circuits in patients with iNPH.