Idiopathic normal pressure hydrocephalus : epidemiology and diagnostics

Abstract: Idiopathic normal pressure hydrocephalus (iNPH) is a progressive neurological condition characterized by a deterioration of gait, cognition, and continence. The diagnosis is based on a combination of enlarged ventricles seen in neuroimaging, with typical clinical findings. iNPH often affects elderly individuals (i.e., over the age of 65). Shunt insertion is the only available treatment, with an improvement rate of up to 80%.The prevalence has previously been reported to be between 0.5 and 3% among individuals over age 65. However, most previous studies have been conducted on hospital-based materials, and there is a lack of epidemiological studies based on the general population. One of the challenges of diagnosing iNPH is that there are no common, widely accepted diagnostic criteria. There are currently two different diagnostic guidelines: the American-European guidelines and the Japanese ones, which makes it harder to compare different studies.The aim of this thesis was to determine the prevalence of iNPH in population-based materials and to evaluate the differences between the diagnostic guidelines. Furthermore, we wanted to assess the quality of life and depressive symptoms among individuals with iNPH compared to those without. In addition, we assessed longitudinal changes in the clinical and radiological findings of iNPH.We asked 1,000 individuals aged 65 and older to participate in the study by answering a questionnaire containing typical iNPH symptoms. We invited all participants who had marked at least two symptoms on the questionnaire for further investigation, in addition to a randomly selected group with fewer than two symptoms. A total of 168 participants underwent clinical examinations and computed tomography (CT) of the brain. We followed up with the same cohort two years later with repeated testing, with the addition of questionnaires on depressive symptoms and quality of life. A total of 122 individuals remained in the 2-year follow-up cohort. The clinical examinations included an iNPH-specific grading scale for symptoms and neurological examinations.The prevalence of iNPH for those 65 years and older was 3.7% according to the American-European guidelines and 1.5% according to the Japanese guidelines. The prevalence was higher for those over age 80, with no differences between the sexes. Furthermore, participants with iNPH had more depressive symptoms and lower quality of life than those without iNPH. Radiological findings and symptoms progressed slightly over two years, and those with symptom deterioration had an even higher degree of radiological progress compared to those with stationary or improved symptoms.This thesis shows that iNPH is fairly common in a normal population of elderly individuals. There is disagreement between the current diagnostic guidelines, which underscores the need for revisions, preferably into one common diagnostic system. In this thesis, individuals with iNPH had a lower functional status, more depressive symptoms, and lower quality of life than those without iNPH.Moreover, iNPH progresses slightly in both symptoms and radiological signs over two years, which underlines the value of clinical follow-up for asymptomatic individuals with radiological signs of iNPH. Finally, iNPH is probably underdiagnosed and an important diagnosis to consider in an elderly person with gait and balance impairments.