As America’s elderly population grows, so does a diagnosis that has lurked quietly in the background: normal pressure hydrocephalus (NPH). A potentially reversible cause of dementia, NPH is marked by abnormal buildup of cerebrospinal fluid (CSF) in the brain’s ventricles. It causes a classic symptom triad—incontinence (“wet”), gait instability (“wobbly”), and cognitive changes (“wacky”). It was first described in 1965 by clinicians who found those three mild impairments in patients who had hydrocephalus with normal CSF pressure. (See Following the flow of cerebrospinal fluid by clicking the PDF icon above.)
Two types of NPH exist:
- idiopathic, which has no clear discernible cause
- secondary, which may stem from hemorrhage, infection, inflammatory conditions, or Paget’s disease of the skull.
NPH is primarily a disease of the elderly. While it isn’t clearly understood, experts suspect it involves impaired CSF absorption and drainage, leading to slow CSF reaccumulation in the ventricles. Although the diagnosis of NPH has been around for nearly 50 years, it’s frequently missed. And because it hasn’t been formally defined, estimated yearly occurrence in the United States ranges widely from 2 million to 20 million.
Signs and symptoms
Careful screening and symptom evaluation allow prompt evaluation and treatment. The subtle signs and symptoms of NPH can be overlooked easily because they resemble those of other disorders. However, NPH may be reversible, making prompt diagnosis crucial. Disorders that may resemble NPH include Alzheimer’s disease, Parkinson’s disease, and Lewy Body dementia. (See An elusive diagnosis by clicking the PDF icon above.) A complete history, physical examination, and review of signs and symptoms are essential for accurate diagnosis.
The term “wet, wobbly, and wacky” can help clinicians remember the symptom triad. Be aware, though, that although many patients exhibit this classic triad, not all three symptoms need be present to establish the diagnosis. Urinary incontinence may arise in later stages of NPH, so urinary urgency and frequency must be differentiated from incontinence. Experts believe urinary symptoms of NPH result from stretching of the periventricular pathways leading from the brain to the bladder. Gait instability coupled with urinary frequency can prevent timely voiding and lead to incontinent episodes. In older adults, urgency and incontinence can be hard to distinguish from other urologic dysfunctions.
Abnormal gait is the most common complaint in NPH. Patients report feeling their feet are “stuck to the ground” as if by a magnet. Difficulty with gait initiation may be attributed to other disorders, such as Parkinson’s or Alzheimer’s disease. Usually, NPH symptoms are bilateral; the patient must take several steps when turning, making a clocklike motion instead of the normal clear pivoting motion.
Cognitive impairment in NPH causes slowing of thoughts, decreased concentration, and an apathetic affect, possibly resembling depression. Gross and fine motor functions become slower and less precise. Family and friends may notice personality and behavioral changes first. Testing reveals slow reaction time and recall, inattention, apathy, and decreased executive functions. Speech volume diminishes, but true aphasia is rare.
Comprehensive multidisciplinary testing is essential for an accurate and timely diagnosis. Radiographic imaging (usually computed tomography) is done first to rule out structural brain disorders. Magnetic resonance imaging (MRI) is more specific and best used to evaluate soft-tissue abnormalities.
The radiographic hallmark of NPH is ventriculomegaly (enlargement) of the lateral ventricles not attributable to other structural defects. Radiographic tests also can identify CSF flow voids (changes in CSF flow in the ventricles). In NPH, the Evans ratio (ratio of the largest width of the frontal horns to the maximal biparietal diameter of the ventricle) exceeds 30%.
Neuropsychological testing can help pinpoint specific functional impairments by evaluating the patient’s word use, speed of speech, memory, and other cognitive abilities. Such testing must be done without the aid of family members to prevent clouding of the patient’s true cognitive ability.
Gait testing by a physical therapist can determine motor strength and gait instability. Specific tests, such as a timed walking test and the Berg Balance scale (which measures functional balance in older adults), also may be done.
Other methods used to evaluate a patient for NPH include intracranial pressure monitoring, CSF dynamic testing, and cisternography using radioisotopes. However, these methods are falling out of favor because they provide only limited diagnostic information.
Two techniques can be used to remove CSF (called CSF diversion) and aid diagnosis.
- High-volume lumbar puncture (LP) removes 30 to 50 mL of CSF. The patient is observed for changes in gait and cognitive function before and after LP. However, this technique doesn’t allow the brain to recover physiologically; also, gait and cognitive changes can be hard to ascertain definitively.
- Continuous CSF drainage over a 3-day period removes a prescribed amount of CSF, usually every 2 hours. It requires an overnight hospital stay. Gait, cognition, and continence are tested before and after drainage. Prolonged drainage of 300 mL or more is associated with a better response than surgical CSF diversion with a permanent shunt.
Surgical CSF diversion with a shunt is recommended for patients with idiopathic NPH. A permanent shunt is inserted surgically into the ventricle down to the peritoneal cavity, where excess CSF is excreted. Other types of shunts, such as a ventriculoatrial or lumboperitoneal shunt, may be used.
In some cases, endoscopic third ventriculostomy is done. The surgeon creates an opening in the floor of the third ventricle to allow CSF to flow directly to the basilar cisterns. Although this technique has yielded some success, pressures commonly found in NPH may not allow permanent patency of the ventriculostomy.
Debate exists over which type of shunt valve—flow-regulated or differential pressure-regulated—promotes the best outcomes The neurosurgeon chooses the device best suited to the patient; in the outpatient setting, follow-up ensures the proper valve setting is used to divert CSF and thus prevent adverse outcomes (such as overdrainage and subdural hematoma). If the shunt is programmed correctly and works as expected, symptoms decrease and quality of life improves.
Patients who have shunts placed commonly stay in the hospital 1 to 2 days to check for infection and monitor neurologic status. Potential shunt complications include subdural hemorrhage, infection, seizures, intracranial hemorrhage, mechanical shunt failure, and surgery-induced abdominal injury. Follow-up medical visits are required to check for these complications.
Certain factors may predict success of CSF shunting. Patients with early onset of a gait disorder, symptom duration less than 6 months, and a positive response to CSF removal are good indicators. Unfavorable indicators are absence of gait disorder, a gait abnormality that arises after dementia manifests, early-onset dementia, dementia for more than 2 years, and marked white-matter atrophy or diffuse atrophy on MRI. Ongoing studies are needed to determine the long-term success of shunts.
Dedicated NPH programs
Hospitals with dedicated, multidisciplinary NPH programs are an asset to communities and can improve patient outcomes. These programs typically offer a 3-day testing model that includes specialized radiographic tests to detect CSF flow problems. Neuropsychological testing can reveal specific aspects of functional impairment involving word use, memory, and other executive functions. A physical therapist evaluates the patient’s motor and gait strength using a timed walking test and the Berg Balance scale. Unfortunately, few dedicated NPH programs exist.
Increased awareness of NPH among both healthcare professionals and the public can promote favorable patient outcomes. Local NPH support groups may be available to provide ongoing support and education for patients and their families. The Hydrocephalus Association offers education, support, and patient advocacy. More research on diagnostic techniques and CSF shunting is needed.
Hydrocephalus statistics. Hydrocephalus Association. http://www.hydroassoc.org/about-us/newsroom/facts-and-stats-2/. Accessed March 8, 2014.
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Misti Tuppeny is a clinical nurse specialist for neuroscience, behavioral health, and rehabilitation at Florida Hospital in Orlando.