Objectives: Because the progression of idiopathic normal pressure hydrocephalus (iNPH) is partially irreversible, we hypothesized that early intervention would markedly improve its prognosis. To test this hypothesis, we retrospectively investigated the long-term prognosis of patients with early intervention in the prodromal phase of iNPH. Methods: We defined the prodromal phase of iNPH as a 3m Timed Up and Go (TUG) of 13.5 s or less and a Mini-Mental State Examination (MMSE) of 24 or more. Of the 83 iNPH patients who underwent shunt surgery at Osaka Medical and Pharmaceutical University Hospital over 3 years from January 2015, 12 prodromal phase cases (73.3 ± 6.2 years, 10 males and 2 females) were included in the study. The iNPH grading scale (INPHGS), MMSE, Frontal Assessment Battery (FAB), intermittent gait disturbance (IGD), social participation status, and development of comorbidities were evaluated over 4 years. Results: Preoperative MMSE was 27.2 ± 1.5, FAB was 14.1 ± 1.8, TUG was 10.7 ± 1.4 s, and total iNPHGS was 2.8 ± 1.4. At 1, 2, 3, and 4 years postoperatively, total INPHGS improved to 0.8, 0.9, 1.5, and 1.7, respectively, and remained significantly better than preoperatively except at 4 years postoperatively. The MMSE improved slightly to 27.5 after 1 year and then declined by 0.35 per year. After 4 years, the mean MMSE was 26.1, and only one patient had an MMSE below 23. FAB improved to 15.2 after 1 year and then declined slowly at 0.85/year. Ten patients (83%) maintained a high capacity for social participation postoperatively. The preoperative tendency to fall and IGD in 9 (75%) and 8 (67%) patients, respectively, completely disappeared postoperatively, resulting in improved mobility. Shunt malfunction associated with four weight fluctuations and one catheter rupture caused temporary worsening of symptoms, which were recovered by valve re-setting and catheter revision, respectively. Conclusion: Early intervention in the prodromal phase of iNPH patients maintained good cognitive and mobility function and social participation ability in the long term. The maintenance of long-term cognitive function suggests its preventive effect on dementia. To realize early intervention for iNPH, it is desirable to establish an early diagnosis system for iNPH.

Corrigendum: Evaluation of the Effectiveness of the Tap Test by Combining the Use of Functional Gait Assessment and Global Rating of Change

Background: Although the tap test for patients with suspected idiopathic normal pressure hydrocephalus (iNPH) is still often performed as part of the preoperative evaluation, it is true that some studies have reported the limitations of the tap test, claiming that it does not provide the additional information for appropriate patient selection for surgery. We aimed to determine whether a better method of pre- and post-tap test assessment could lead to appropriate patient selection for shunting. Methods: We performed the tap test as part of the preoperative evaluation in all 40 patients who underwent lumboperitoneal shunt surgery for iNPH from April 2021 to September 2021. We retrospectively analyzed the patient data. We examined whether a comprehensive evaluation of the effect of the tap test using the Functional Gait Assessment (FGA) and Global Rating of Change (GRC) scales would identify a wider range of patients who would benefit from shunt surgery than the 3-m Timed Up and Go test (TUG) alone. Results: Assuming a prevalence of 1% for iNPH, the TUG had a sensitivity of 0.23, specificity of 0.71, positive likelihood ratio of 0.79, and negative likelihood ratio of 1.09. When improvement in either the FGA or the GRC was used as a criterion for the validity of the tap test, the sensitivity was 0.88, specificity was 0.17, positive likelihood ratio was 1.06, and negative likelihood ratio was 0.71. Conclusion: Improvement in either the FGA or the GRC is a more sensitive criterion for the effectiveness of the tap test for the gait aspect than the TUG. Since the negative likelihood ratio is lower than that for the TUG alone, it is more appropriate to exclude patients with neither FGA nor GRC improvement from surgical indications than to exclude surgical indications based on a negative TUG.

Cerebral autoregulation is a robust regulatory mechanism that stabilizes cerebral blood flow in response to reduced blood pressure, thereby preventing cerebral ischaemia. Scientists have long believed that cerebral autoregulation also stabilizes cerebral blood flow against increases in intracranial pressure, which is another component that determines cerebral perfusion pressure. However, this idea was inconsistent with the complex pathogenesis of normal pressure hydrocephalus, which includes components of chronic cerebral ischaemia due to mild increases in intracranial pressure. Twenty-one patients who underwent ventriculoperitoneal shunt surgery for normal pressure hydrocephalus were included in this study. To determine the pressure setting of the Codman-Hakim programmable valve, intracranial pressure was measured after shunt surgery by puncturing the Ommaya reservoir, which formed a closed circuit with the needle and the syringe. Then, intracranial pressure was continuously measured with intermittent infusion of cerebrospinal fluid from the same closed circuit. We also continuously measured oximetry data, such as regional cerebral oxygen saturation derived from near-infrared spectroscopy monitoring. These data were digitized, recorded, and used for calculating intracranial compliance and the relationship between cerebrospinal fluid volume loading and intracranial pressure. This study demonstrates that in patients with normal pressure hydrocephalus, cerebral venous vascular bed compression induces mild cerebral ischaemia when intracranial pressure is slightly higher than physiological venous pressure. Cerebral venous compression impairs cerebral blood flow by quadratically increasing circulatory resistance according to Poiseuille’s law. Furthermore, chronic cerebral ischaemia occurred even at low or normal intracranial pressures when deep and subcortical white matter hyperintensities (DSWMHs) were severe. The fact that cerebral blood flow impairment begins at very low intracranial pressures indicates that cerebral autoregulation to compensate for reduced venous blood flow is not functioning adequately in NPH. These processes provide a link between impaired cerebrospinal fluid circulation, cerebral autoregulation, and neurological dysfunction, which has been missing in patients with NPH involving small vessel arteriosclerosis. These findings may provide insight into similar conditions, such as normal-tension glaucoma and chronic kidney disease, in which a mild increase in local compartment pressure leads to chronic ischemia in organs protected by autoregulatory mechanisms.

Objectives: We identified a new type of shunt malfunction (SM) in patients with normal pressure hydrocephalus (NPH). It is induced by weight change and can be treated with valve readjustment. There were two types of SM as follows: Underdrainage induced by the weight gain and overdrainage induced by the weight loss. This study aims to elucidate this mechanism by assessing the shunt pressure environment.Methods: The total pressure environment of the shunt system was prospectively studied in patients with shunted NPH at Osaka Medical College Hospital from 1999 to 2005. We measured the pressure environment during the initial pressure setting of the valve by the intracranial pressure (ICP) guide, after setting the valve, and when SM was suspected. We evaluated ICP, intra-abdominal pressure (IAP), and hydrostatic and perfusion pressures of the shunt system in the sitting and supine positions. The target ICP for valve setting was empirically set at the range from −8 to −13 mm Hg in the sitting position, referring to the external auditory meatus. During the study period, we identified five cases of SM induced by weight change and assessed the changes in the pressure environment across pre-SM, SM, and post-SM.Results: In four cases of underdrainage, gait disturbance worsened with an average weight gain of 6.8 ± 1.2 kg. With weight gain, IAP and ICP increased by 8.8 ± 1.6 and 4.8 ± 1.0 mm Hg, respectively. Consequently, ICP increased to −6.5 ± 1.9 mm Hg. One overdrainage patient developed an asymptomatic chronic subdural hematoma (CSDH) with a weight loss of 10 kg. With the weight loss, both IAP and ICP decreased by 5 mm Hg, and concomitantly, ICP decreased to −18 mm Hg. In all patients, the valve readjustment restored their ICP to the target pressure. After the valve readjustment, the gait disturbance improved immediately, and the CSDH disappeared after 1 month.Conclusion: In patients with shunts, the weight change was linked to ICP via IAP. Due to the weight change, the underdrainage occurred when ICP was above the target pressure, and the overdrainage occurred when ICP was below it. We named this SM as the weight and abdominal pressure-induced shunt trouble. The patients with SM along with weight changes should be the first to be tried for the valve readjustment.