Normal Pressure Hydrocephalus
Normal pressure hydrocephalus (NPH) is a brain disorder in which excess cerebrospinal fluid accumulates in cavities of the brain called ventricles, causing cognitive problems including thinking and reasoning problems, difficulty walking and loss of bladder control.
NPH is called "normal pressure" because despite the excess fluid, cerebrospinal fluid pressure (measured during a spinal tap), is often normal. As brain ventricles enlarge with the excess cerebrospinal fluid, they can disrupt and damage nearby brain tissue, causing symptoms of NPH.
Who gets NPH?
Several recent epidemiological studies confirm that NPH is a rare disease, though the presence of large ventricles is a common finding with ageing. In a large population-based sample using neuroimaging and clinical examination, researchers found that the prevalence of probable NPH was 0.2 per cent in persons between the ages of 70 to 79 years of age, and 5.9 per cent in those older than 80 years of age.
However, NPH primarily affects people in their 60s and 70s. We do not know the exact prevalence of NPH, because common symptoms of NPH are also common in other brain disorders.
What causes NPH?
It may result from a subarachnoid haemorrhage (bleeding inside the brain), head trauma, infection, tumour, or complications of surgery. However, many people develop NPH even when none of these factors are present. In these cases, the cause of the disorder is unknown (idiopathic NPH).
What are the symptoms of NPH?
The hallmark symptoms of normal pressure hydrocephalus include:
- A decline in cognitive skills, in the form of mild dementia that involves loss of interest in daily activities, forgetfulness, difficulty completing routine tasks and short-term memory loss.
- A decline in thinking skills that include overall slowing of thought processes, apathy, impaired planning and decision-making, reduced concentration, and changes in personality and behaviour are other features.
- Difficulty walking- sometimes compared to the way a person walks "on a boat," with the body bent forward, small steps, legs held wide apart, feet moving as if they're "glued to the deck”, and difficulty making turns.
- Urinary urgency followed by loss of bladder control, which tends to appear somewhat later in the disease than difficulty walking and cognitive decline.
How is NPH diagnosed?
There is no single test that is diagnostic of normal pressure hydrocephalus. Although the three hallmark symptoms of cognitive decline, walking difficulty and loss of bladder control are considered the classic signs of this disorder, not everyone with NPH has all of these symptoms.
Brain imaging to detect enlargement of the ventricles, often with magnetic resonance imaging (MRI), plays a key role in diagnosing NPH. Several brain disorders, including Alzheimer's disease, can cause overall brain tissue shrinkage that makes the ventricles look larger than normal. In NPH, although the ventricles are enlarged, brain tissue may not appear shrunken.
Since the symptoms of NPH may overlap with those of Alzheimer's and other dementias, it is recommended that a person with suspected NPH undergo examination by a neurologist experienced in evaluating brain disorders that affect movement, thinking skills and physical functions. FDG PET may serve as a useful diagnostic biomarker in evaluating a person for NPH.
While AD pathology is an important comorbid disease confounding the cognitive features of NPH, Parkinson disease and other neurodegenerative parkinsonian syndromes causing walking or gait abnormality are important conditions to consider when evaluating NPH.
Besides showing reduced metabolism that is characteristic of AD, FDG-PET is abnormal in a wide range of neurodegenerative diseases. A finding of reduced metabolism in the caudate lobe of the brain has been identified as a potential biomarker in NPH.
If symptoms and CT/ MRI/FDG-PET are suggestive of NPH, a large-volume spinal tap may be used to identify those who may benefit from a shunt. Here, the doctors remove a large amount of spinal fluid and then observe the person for 30 to 60 minutes to note any improvements in walking or thinking and reasoning. Most people originally suspected of having NPH does not improve following a CSF removal test.
In some cases, normal pressure hydrocephalus is caused by other brain disorders such as haemorrhages, infections or inflammation. But in most cases, the cause of fluid accumulation is unknown.
Treatment and outcomes
Unfortunately, there are no effective nonsurgical treatments available for normal pressure hydrocephalus at this time. Drugs, such as diuretics that remove excess fluid from the body, have not been found to be effective.
NPH can sometimes be treated with surgical insertion of a shunt, a long, thin tube that drains excess CSF from the brain to the abdomen. Difficulty walking is the symptom most likely to improve after surgery. Cognitive changes and bladder control are less likely to get better. Shunting does not help everyone with NPH, and there is uncertainty about how best to identify those most likely to benefit.
More research is needed to understand the prevalence of NPH, clarify the benefits of shunt insertion and identify those likely to benefit.
The effectiveness of shunting in NPH has not been established in a randomized clinical trial. Most of these studies were small and followed people for a limited time. Available data suggest that difficulty walking is the symptom most likely to improve. Some studies showed that the short-term benefits of shunt insertion tended to decline over time. Other studies found a significant rate of postsurgical complications.
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