Epidemiology of Idiopathic Normal Pressure Hydrocephalus

Michael J. Fritsch

2.1 Epidemiologic Studies

2.1.1 Trenkwalder et al (1995)

In 1995, Trenkwalder et al conducted one of the first and most quoted studies.¹ The aim of the study was to investigate the prevalence of different types of Parkinson disease (PD) in elderly patients. The study was conducted by going door-to-door in two Bavarian villages and surveying 982 participants. Individuals older than 65 years were included. Following a screening questionnaire and motor testing, all individuals suspected of having PD were reinvestigated by a neurologist and underwent a computed tomography (CT) scan. The prevalence of PD in this study group was 0.71% and—as an unexpected finding—the prevalence of normal pressure hydrocephalus (NPH) was 0.41% (4/982). No further diagnostic work-up or treatment was attempted.

The study was performed 18 years ago. Magnetic resonance imaging (MRI) has brought further insight into the diagnosis of hydrocephalus, and the age distribution of the German population has changed—one would expect a higher prevalence of NPH if this study were repeated today.

2.1.2 Tisell et al (2005)

Tisell et al determined that the annual incidence of surgery for adult hydrocephalus in Sweden was 3.4 per 100,000 between the years 1996 and 1998.² The most common indication for surgery was NPH (47%). The resulting incidence for NPH was 1.598 (47% of 3.4) per 100,000 each year.

2.1.3 Marmarou et al (2007)

Marmarou et al wanted to estimate the prevalence of idiopathic NPH (iNPH) among residents of two assisted-living and two extended-care facilities.³ Patients who were 85 years or older were excluded. In a retrospective chart review, the analysis included 147 patients. Overall, 14.7% of the patients had symptoms of gait disturbance and incontinence, and 9.4% had symptoms of gait disturbance and dementia. A total of 11 of the 147 patients (7.5%) had a complete Hakim triad. The authors assumed that gait disturbance plus incontinence, dementia, or both was necessary for a clinical diagnosis of iNPH; therefore, they concluded that the overall prevalence of the disease ranged from approximately 9% to 14%.

However, of the 147 patients included in the survey, only 5 had undergone MRI or CT imaging. The discrepancy between clinical findings and (attempted) imaging, according to the authors, suggests that iNPH symptoms are often overlooked.

There are limitations to this study including the almost negligible number of patients who underwent imaging and further clinical evaluation. Among a subset of 17 patients who underwent a standard iNPH diagnostic and management protocol, 11 received a shunt.

2.1.4 Hiraoka et al (2008)

Hiraoka et al examined the prevalence of iNPH in the elderly population of a Japanese rural community.⁴ They selected 2,053 residents aged 65 years or older to complete a health questionnaire. From this group, 240 people were randomly selected for an MRI examination. Of these 240 people, only 200 underwent MRI, and 170 underwent a neurologic examination and neuropsychological testing. The 40 participants who did not undergo MRI were unable to do so because of diseases, immobility, or other physical problems. Patients with an Evans index of 0.3 or greater and narrowing of the cerebrospinal fluid (CSF) space at the convexity and midline area were considered to be positive for ventricular enlargement. Those who underwent MRI were screened for clinical signs and symptoms of iNPH. Within the group of 170 who were examined, 5 (2.9%) demonstrated ventricular enlargement and cognitive impairment (5/5), and 1 of these five showed gait disturbance (1/5), and 1 showed urinary incontinence (1/5). The authors concluded that there was a 2.9% prevalence of iNPH in the elderly population aged 65 years or older.

This study has several limitations. First, the majority of the 40 participants not examined were 80 years of age or older and in poor physical condition. Among these 40, there were probably more people who would have fulfilled the criteria for iNPH. Second, no CSF tap test, lumbar drainage test, or CSF shunting was performed in any of the patients. Therefore, there is no clinical confirmation of the diagnosis of iNPH. Third, the distribution of symptoms (five participants with dementia, including one with gait disturbance, and one with urinary incontinence) is atypical for iNPH. One would expect to find gait disturbances in almost all of these patients.

2.1.5 Brean and Eide (2008)

Brean and Eide examined the prevalence of iNPH in Norway in 2008.⁵ In a population of 220,000 inhabitants, intense efforts were directed to the public and to health care professionals to recruit and refer patients with iNPH during a 12-month period. The task was supported by the fact that the population of 220,000 was served by one single neurological department and one single neurosurgical department. Within the 12-month period, 86 patients were referred for evaluation of NPH. Out of those, 48 patients fulfilled the criteria for NPH based on imaging and clinical examination.

Based on these data, the minimum prevalence of iNPH in the Norwegian population was calculated as 21.9 per 100,000 cases. The incidence for the 12-month period was found to be 5.5 per 100,000 cases per year. The authors concluded that these numbers represent the minimum estimates.

The limitation of this study—which is similar to that of Tisell et al’s study in Sweden—is that only referred patients were evaluated.² This excludes the population that was simply not evaluated (probably the majority) as well as part of the population that was treated outside of the area.

2.1.6 Brean et al (2009)

In a follow-up study in 2009, Brean et al retrospectively collected data on patients who were hospitalized from 2002 to 2006 with a diagnosis of iNPH in one of five neurosurgical centers in Norway.⁶ During the 5-year period, 252 patients underwent operations for iNPH.

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