Normal Pressure Hydrocephalus (NPH) is a neurological condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within the brain’s ventricles. This buildup causes the ventricles to enlarge, placing pressure on surrounding brain tissue. While the term “normal pressure” might seem counterintuitive, it refers to the fact that the pressure inside the skull is often within the normal range, or only slightly elevated, despite the fluid buildup. NPH typically manifests through a combination of three main symptoms: difficulties with walking, changes in thinking abilities, and problems with bladder control.
Prevalence and Incidence
Prevalence refers to the total number of existing cases in a population at a specific time, while incidence indicates the rate of new cases developing over a period. Estimates for NPH vary due to differences in diagnostic methods and populations studied.
NPH is considered relatively uncommon but affects a significant number of older adults. For individuals aged 70 to 79, prevalence is estimated at 0.2%. This figure rises to approximately 5.9% for people aged 80 and above. The Hydrocephalus Association estimates nearly 700,000 adults in the United States may have NPH.
Incidence rates also demonstrate an age-related increase. Overall rates range from 1.8 to 7.3 new cases per 100,000 people per year. For those aged 70 and older, incidence can be as high as 1.2 per 1,000 people annually. Despite these figures, NPH is likely underdiagnosed, suggesting the actual number of affected individuals could be higher.
Demographic Considerations
NPH primarily affects older adults, with symptom onset typically around 70 years. It is rare in individuals under 65, affecting only about 0.003% of that age group.
While some studies show no significant differences in prevalence between men and women, other data suggests a slight male preponderance in certain age groups (e.g., 2.1% for men vs. 0.96% for women among 70-year-olds). In many cases, the cause of NPH remains unknown, termed idiopathic NPH, accounting for roughly half of all occurrences. NPH can also develop as a secondary condition following other medical events.
Risk factors for secondary NPH include brain trauma, brain hemorrhage, brain infections (like meningitis), brain tumors, and complications from prior brain surgery. For idiopathic NPH, vascular risk factors include hypertension, diabetes mellitus, coronary heart disease, and being overweight.
Challenges in Diagnosis
Diagnosing NPH presents significant challenges, contributing to its frequent underrecognition and misdiagnosis. NPH symptoms—gait difficulties, cognitive impairment, and urinary incontinence—are often subtle and can closely resemble those of other common conditions in older adults, leading to confusion with general aging or neurodegenerative diseases like Alzheimer’s and Parkinson’s. This overlap means less than 20% of individuals with NPH are properly diagnosed, with many cases mistakenly attributed to other ailments.
The gradual onset and progression of NPH symptoms further complicate diagnosis. While a classic triad of symptoms is recognized, not all three may appear simultaneously or develop over an extended period. Gait disturbance is typically the earliest and most prevalent symptom.
The diagnostic process often involves brain imaging, such as MRI or CT scans, to identify enlarged ventricles. However, enlarged ventricles can also be observed in other conditions, including Alzheimer’s disease, requiring careful interpretation. A cerebrospinal fluid (CSF) tap test, or lumbar puncture, is another diagnostic tool where a small amount of CSF is removed to see if symptoms temporarily improve, which can indicate NPH. The absence of universally standardized diagnostic criteria further adds to the complexity, making NPH a condition that often goes undiagnosed despite being potentially treatable.