Postural function in idiopathic normal pressure hydrocephalus before and after shunt surgery: A controlled study using computerized dynamic posturography (EquiTest)

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Abstract

Introduction

Postural dysfunction is one of the major features of idiopathic normal pressure hydrocephalus (iNPH). With computerized dynamic posturography (CDP) balance can be assessed objectively. The primary aim of this study was to describe the postural function in iNPH patients pre- and post-operatively in comparison with healthy individuals (HI) using CDP.

Subjects and methods

Thirty-five patients (16 M, 19 F) with a mean age of 73 (range 49–81) with iNPH, and sixteen HI (7 M, 9 F) aged 73 (62–89) were included. iNPH patients were operated on with a ventriculo-peritoneal shunt. Patients and HI were tested regarding motor function, balance and cognition. CDP, EquiTest (NeuroCom International, Clackamas, OR), was performed before and three months after shunt surgery and twice in HI, with a three-month interval.

Results

Pre-operatively, the 35 patients had poorer balance measured with the Sensory Organizing Test (SOT) score in every condition (p = 0.01 in SOT 1 and p < 0.001 in SOT 2–6) compared to the HI. The greatest difference was in test conditions measuring mainly vestibular function, where loss of balance (LOB) was frequent. Twenty patients were evaluated three months after shunt surgery and 18/20 (90%) of them were considered shunt responders, with a mean improvement of motor score of 26% (range 5–67%). There was an improvement post-operatively in the weighted composite SOT score (p < 0.05) but no significant change in any of the SOT conditions. LOB was not significantly reduced in any of the test conditions.

Conclusion

CDP showed that the patients had a poorer balance than the HI. The greatest difference was in SOT 5–6, indicating that the postural disturbance is of primarily central vestibular origin. There was a slight improvement of balance post-operatively.

Introduction

Postural disturbance is an important symptom of idiopathic normal pressure hydrocephalus (iNPH) and is, together with the motor dysfunction, responsible for the most striking symptom, namely gait difficulties [1]. The other classical symptoms of iNPH are impaired cognition and urinary urgency [1]. The symptoms usually exist together, but the severity may range from subtle to disabling [2]. iNPH usually affects older individuals with a mean age of around 70 y [3], [4] and the prevalence has been estimated to be as high as 1.4% in elderly Japanese people [5]. iNPH is characterized by a ventricular enlargement secondary to a cerebrospinal fluid (CSF) disturbance, where the CSF-pressure is within the normal limits. There have been a few studies addressing the issue of postural dysfunction in iNPH. Soelberg-Sörensen et al. found a decreased postural stability [6] and Blomsterwall et al. went further and concluded that postural dysfunction is partly responsible for the gait difficulties, and that improvement after shunt surgery is more profound in tests assessing balance [7]. In a later study, Blomsterwall et al. used a force platform to assess balance in patients with normal pressure hydrocephalus (NPH) and subcortical arteriosclerotic encephalopathy. In this study, no difference regarding balance could be detected between the groups of patients, but compared to HI the hydrocephalic patients had significantly larger sway area and showed higher backward velocity [8].

Postural function is dependent on vision, peripheral vestibular sense, proprioception and a central integration. With advancing age there is impairment in these functions, and if there is a selective impairment in one of them, greater demands are placed on the remaining functions in order to maintain a good balance [9]. It is of great importance to assess balance in the elderly properly to identify individuals at risk of falling, since the consequences of traumatic injuries can be enormous, both for the individual and also for society.

There are many bedside clinical tests for assessing balance. The oldest, and one that is still performed, is Romberg's test [10], other examples are the Tinetti balance and gait test [11] and the Berg Functional Balance Scale [12]. They are easy to perform but have the problems of ceiling effects and poor specificity [13].

Instrumental methods have been developed for assessing balance more accurately. Computerized dynamic posturography (CDP) is a method involving the measurement of ground reaction forces from which the centre of pressure and sway may be calculated [14]. The simplest equipment is a force plate. A more advanced equipment is EquiTest (version 4.04 NeuroCom International, Clackamas, OR); a diagnostic tool that measures the sway in several conditions. CDP can potentially differentiate between different causes of postural dysfunction, such as vestibular, proprioceptive and visual. The method has never been used before to evaluate patients with hydrocephalus.

The primary aim of this study was to describe the postural function in iNPH patients by CDP pre-and post-operatively and in comparison with HI.

Section snippets

Subjects and methods

Thirty-five patients (16 males, 19 females) with mean age 73 (49–81) (Table 1) diagnosed as probable iNPH with modified iNPH guidelines [1] were consecutively included. They were recruited from the outpatient clinic of Neurology, University of Linköping.

Clinically there had to be a gait disturbance affecting both legs, including difficulties with tandem walking, multistep turning, decreased step length and a straddled gait where no other condition could be the cause. Patients with neurological

Healthy individuals

Sixteen HI (7 males, 9 females) aged 73 (62–89) were consecutively recruited mainly from relatives and friends to staff members (Table 1). They were subjectively healthy and had a normal gait, balance and cognition on examination. Medication and diseases not impairing gait and cognitive status were not considered reasons for exclusion.

Results

The 35 patients had lower SOT scores in all six conditions (p = 0.01 for SOT 1 for SOT 2–6 p < 0.001) before surgery compared to the HI. The greatest difference was in conditions 5 and 6 (Fig. 2). LOB was very frequent in SOT conditions 5 and 6 in iNPH pre-operatively and thus very significantly different from the HI (Fig. 3). Pre-operatively, the patients showed significantly inferior gait capacity, had lower score in the Romberg's test, and performed a lower MMSE than the HI (Table 2).

Discussion

The main findings of this study are that the iNPH-patients had significantly poorer balance than HI in all SOT conditions, and this was most pronounced in SOT 5 and 6, indicating a central vestibular dysfunction in iNPH patients. Loss of balance was also seen most frequently in conditions 5 and 6. However, improvement after shunt could only be seen as a significant change of the composite SOT but not in any individual condition.

The patients who participated in this study were all diagnosed as

Conclusion

For the first time CDP with the SOT protocol has been used to evaluate patients with iNPH. The patients showed a profound disturbance of postural function compared to HI, and this disturbance was probably caused by deficient central integration of vestibular function. There was a weak improvement in balance three months post-operatively.

Acknowledgements

Physiotherapist Johanna Rydja and Occupational therapist Katarina Owen are kindly acknowledged for their assessments of motor and cognitive function, respectively.

Vestibular assistant Lisbeth Noaksson and Sofie Danielsson are gratefully acknowledged for examining the subjects with CDP.

Natus Medical Inc. is acknowledged for the illustration in Fig. 1 of Sensory Organizing Test.

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