Normal pressure hydrocephalus, or NPH, is a neurological condition that primarily affects older adults. It arises from an accumulation of cerebrospinal fluid (CSF) within the brain’s fluid-filled chambers, known as ventricles. This buildup causes the ventricles to enlarge, which in turn puts pressure on and damages surrounding brain tissue. Despite the excess fluid, the pressure measured during a diagnostic procedure often registers within the normal range, which is why the condition is termed “normal pressure” hydrocephalus. Recognizing NPH is important because, unlike many other conditions with similar symptoms, it is often treatable.
The Triad of Symptoms
The clinical presentation of NPH is defined by three primary symptoms that emerge and worsen over several months. This collection of symptoms affects a person’s ability to walk, think, and control their bladder.
The first and most common symptom to appear is a disturbance in gait. Individuals often develop a slow, short-stepped, and wide-based walk, sometimes described as a “magnetic gait.” This term reflects how the feet seem stuck to the floor, making it difficult to initiate steps or make turns. This instability and poor balance frequently lead to falls.
Cognitive impairment is another component of the triad. This often manifests as mild dementia, characterized by forgetfulness, slowed thinking, and a loss of interest or apathy. Individuals may have difficulty with planning, decision-making, and multitasking. The cognitive changes in NPH are often related to a reduction in attention and executive function, rather than the profound memory loss seen in other dementias.
The final element of the triad is a loss of bladder control, ranging from urinary frequency and urgency to complete incontinence. While all three symptoms are characteristic, they may not appear at the same time or with the same severity. Gait disturbance is typically the first to become prominent.
Causes and Risk Factors
The origins of NPH are categorized into two types. Both stem from the same underlying issue: cerebrospinal fluid is not properly reabsorbed into the bloodstream, leading to its accumulation in the ventricles.
In most cases, the cause for the impaired CSF absorption is unknown; this is referred to as idiopathic NPH. As the most common form, it typically develops in individuals over 60, making advanced age the primary risk factor. Researchers have associated idiopathic NPH with conditions like hypertension and diabetes, but a direct causal link has not been established.
A smaller percentage of cases are classified as secondary NPH, which develops as a result of a known medical event that impedes CSF drainage. Potential causes include:
- Traumatic head injury
- A subarachnoid hemorrhage (bleeding around the brain)
- Complications from brain surgery
- Infections that affect the brain, such as meningitis
- Brain tumors
The Diagnostic Process
Diagnosing NPH involves a multi-step process to observe its signs and rule out other conditions. The evaluation begins with a review of the patient’s medical history and a neurological exam to assess muscle strength, reflexes, and balance. This assessment includes a gait evaluation, where a doctor observes the person’s walking pattern for abnormalities associated with NPH.
Brain imaging is a standard part of the diagnostic process. Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans are used to visualize the brain’s structure and can reveal enlarged ventricles. Imaging also helps exclude other potential causes of the symptoms, such as a brain tumor or stroke. A specific MRI pattern known as DESH (disproportionately enlarged subarachnoid space hydrocephalus) is particularly indicative of NPH.
A large-volume lumbar puncture, or spinal tap, is a definitive diagnostic procedure. During this test, a physician withdraws a significant amount of CSF from the lower back. The patient’s gait and cognitive functions are tested before and after the fluid removal. A marked improvement in walking or cognitive speed after the procedure is a strong predictor that the patient has NPH and will respond well to treatment.
If a single spinal tap is inconclusive, an extended lumbar drainage trial may be performed. This involves hospitalizing the patient for several days to continuously drain CSF through a temporary catheter. This process mimics the effect of a permanent treatment, and symptom improvement during the trial helps confirm the diagnosis and predict a positive surgical outcome.
Shunt Surgery as Primary Treatment
The standard treatment for NPH is the surgical implantation of a device called a shunt. This medical device diverts excess cerebrospinal fluid from the brain’s ventricles to another part of the body where it can be absorbed. This process alleviates the symptoms caused by ventricular enlargement.
A shunt is a thin, flexible tube system implanted beneath the skin. The most common type is a ventriculoperitoneal (VP) shunt, which has a catheter placed into a brain ventricle. This catheter connects to a valve that regulates fluid drainage and a longer tube that is tunneled to the abdominal cavity. The excess CSF flows through this system and is released into the peritoneum to be absorbed by the body.
Shunt surgery effectiveness varies, but many patients experience relief from their symptoms. Gait problems often show the most substantial and earliest improvement. Improvements in bladder control and cognitive function are also possible but can be less predictable and take longer to appear. Patients with idiopathic NPH have an improvement rate between 30 and 50 percent, while those with secondary NPH have a success rate of 50 to 70 percent. Early diagnosis and treatment lead to better outcomes.
Distinguishing NPH from Similar Conditions
The symptoms of NPH can resemble other neurodegenerative disorders common in older adults, leading to misdiagnosis. Differentiating NPH from conditions like Alzheimer’s and Parkinson’s disease is necessary for proper treatment, as NPH is potentially reversible while the others are not.
A distinction between NPH and Alzheimer’s disease is the initial sequence of symptoms. In NPH, problems with walking and balance appear early and are the most prominent feature, while cognitive decline may be milder. In Alzheimer’s disease, memory loss and language difficulties are typically the first signs, with major gait problems developing later in the disease’s progression.
Gait is also a distinguishing factor when comparing NPH to Parkinson’s disease. While both conditions cause walking difficulties, the “magnetic” gait is more characteristic of NPH. Parkinson’s disease is often associated with a resting tremor and rigidity, which are not features of NPH. Patients with Parkinson’s also respond to medications like L-Dopa, which is not the case for individuals with NPH.