Normal Pressure Hydrocephalus Is Oft-Mischaracterized

The term hydrocephalus comes from the Greek words “hydro” meaning water and “cephalus” meaning head, leading the condition to be referred to by laypersons as “water on the brain.” However, the primary characteristic of normal pressure hydrocephalus (NPH) is chronic and excessive accumulation of cerebro-spinal fluid (CSF) in the ventricles of the brain.

Epidemiology

The classic triad of gait difficulties, urinary incontinence, and mental decline that are the hallmark of NPH was first described by Adams and Hakim in 1965. There are no definitive statistics for the prevalence of NPH in the United States. Some experts estimate that up to 750,000 Americans may have NPH. NPH may be the cause for up to 5 percent of dementia diagnoses. Population-based studies have estimated the prevalence of NPH to be about 0.5 percent in those over 65 years old, with an incidence of about 5.5 patients per 100,000 people per year.

Demographics

NPH occurs at about the same frequency in men and women and there is no correlation between NPH and race. NPH can occur at any age, but it is most commonly diagnosed in the senior population. In general, NPH most often affects patients over the age of 50, with the majority being age 60 or older. One recent study estimates that the prevalence of diagnosed and undiagnosed NPH among residents of assisted-living facilities is between 9 to 14 percent. Dementia is the number-one precipitator of nursing home placement. These statistics are important because a patient with dementia who has undiagnosed NPH may become independent again if treated.

Risk Factors

There are two forms of NPH. The secondary form has known risk factors, including: subarachnoid hemorrhage, head injury, brain surgery, stroke, meningitis and brain tumors. The more common form is idiopathic NPH, where the underlying cause is not known.

Prognosis

If NPH is untreated the symptoms (ataxia, dementia and incontinence) will generally worsen over time and it can lead to death. Prognosis is often dependent on whether or not the patient is a candidate for shunting and the success of the shunting. However, statistics regarding the success of shunt surgery are highly variable. Some patients with NPH will have near-complete reversal of symptoms while others will not experience significant improvements from shunting. Studies have demonstrated that patients with secondary NPH have better shunting outcomes (50-70 percent) than those with idiopathic NPH (30-50 percent). Shunts are associated with complication rates of 30-40 percent. Patients who are not candidates for surgery may have temporary improvements in symptoms with periodic lumbar punctures.

Pathophysiology

Physiologic changes in NPH include an increase in the resistance to the reabsorption of CSF, a change in the location of CSF reabsorption from the arachnoid granulations to the deep brain, altered CSF flow, reduced compliance of the subarachnoid space, a normal CSF pressure but increased CSF pulse pressure, an overall reduction in cerebral blood flow and ventricular dilation.

Differential Diagnosis

Dementia is defined as a progressive loss of nerve cells that are responsible for normal thought, memory and daily functioning. The establishment of an NPH diagnosis is accomplished by a detailed history and physical, neuroimaging and laboratory studies. Together, these methods accurately diagnose 90 percent of dementias.

Ten to 15 percent of dementia diagnoses are due to reversible causes, one of which is NPH. Other reversible causes include metabolic abnormalities, nutritional deficiencies, vasculitis, infection, intoxication, anatomical causes such as intracranial masses and bleeding. See Table 1 for suggested laboratory workup for potentially reversible causes of dementia.

Table 1: Dementia Work-up

The best diagnostic tool for diagnosing dementia is a thorough history. In addition, several geriatric assessment tools are helpful. These include: a Mini Mental Status Exam (MMSE), Geriatric Depression Scale (GDS), Activities of Daily Living (ADL) and Instrumental Activities of Daily Living (IADL) inventories, a medication review, as well as hearing, vision and nutrition screenings.

The Mini Mental Status Exam (MMSE) is scored out of a possible 30. A score of over 23 is considered normal, 20-23 is mild, 10-19 moderate, and less than 10 indicates severe dementia. The clock draw test is another useful tool. These tests need a baseline for which comparison can be made to establish the presence of a decline.

The lower the ADL and IADL score the greater the degree of dependence. A total score of less than nine indicates dependency in either inventory.
Depression is known to be a leading cause of pseudo-dementia. There are several accepted GDS’s; a Yesavage 30-point and Yesavage 15-point scales are the most widely accepted. On the 15 point scale a score of greater than one suggests depression. Additionally, the single question “do you often feel sad or depressed” is statistically significant for the diagnosis of depression.

It is important to note that these tests may be administered by any trained health professional, not necessarily a physician.

Definitive Diagnosis

NPH should be suspected when the patient presents with Adam’s triad: urinary incontinence, gait disturbance and dementia. An easy way to remember this triad is “wet, wobbly and wacky.”

Neuroimaging studies such as CT and MRI can be helpful to make the diagnosis. The ventricles will appear enlarged without the presence of flattened sulci that are associated with increased intracranial pressure. See the above image.

In September 2005 an international team of scientists developed clinical guidelines to help physicians diagnose NPH. They recommended that idiopathic NPH be classified into “probable,” “possible” and “unlikely” categories.

Clinical Course

Gait disturbance or ataxia is usually the first symptom of the triad to appear. Gait disturbance can vary depending on the length of time the patient has had NPH. The classic gait disturbance of NPH is described as a “magnetic gait,” in which the feet appear to be stuck to the floor until overcome with an upward and forward motion of each step. A wide stance or broad-based gait is often seen as the patient attempts to compensate for the ataxia.

The next symptom to appear is dementia. The dementia-associated NPH is subcortical, predominantly frontal lobe in nature. This appears as apathy, flat affect and inattention. Memory problems are predominant, which can lead to the misdiagnosis of Alzheimer’s disease. However, in NPH there may be an obvious discrepancy where recall and attention are more affected than recognition, word formation and multistep tasks, differentiating the dementia of NPH from Alzheimer’s.

Urinary incontinence appears later in the course, with symptoms of both increased frequency and urgency.

Prevention

The cause of most cases of NPH is idiopathic. However, steps can be taken that reduce the risk factors of secondary NPH including head injury and stroke which can result in NPH. Chances of head injury can be decreased by wearing a safety belt when driving or a passenger in an automobile and wearing a safety helmet when biking, skiing or engaging in other activities where falls and head trauma are common. Not smoking, eating a healthy diet, and being physically active reduce the risks of hypertension and diabetes, which are risk factors for stroke.

Treatment

Currently there are no medications to treat NPH. The most common treatment is to surgically place a ventriculoperitoneal (VP) shunt. Placement of a VP shunt is a surgical procedure in which a neurosurgeon implants a thin tube that originates in the enlarged ventricle in the brain into the peritoneal cavity in the patient’s abdomen where the CSF can be safely absorbed through the peritoneum into the bloodstream. Attached to the tube is a small valve that opens when CSF pressure builds up. The flow of CSF is monitored to see if adjustments to the valve are needed. Newer valve technology allows the neurosurgeon to adjust the valve externally, so additional surgery is not required.

Because not all patients with NPH are suitable candidates for shunt surgery, proper diagnostic testing for NPH is essential to determine if a patient is suitable. (See Table 2.) Patients who are not surgical candidates may be considered for periodic lumbar punctures, which provide some relief of symptoms.

Table 2: Prediction of Shunt Response

Case Management Implications

Knowing the classic symptoms of NPH will help the case manager be aware of the risks patients face with the condition. Falls prevention is a focus for gait disturbance. An environmental assessment is conducted and all environmental falls risks identified. Shoes that are lightweight with firm support are helpful, as is avoiding slip-on shoes. Lightweight furniture and cords across walkways should also be avoided. Adaptive equipment such as grab bars, shower chairs and a walk-in shower are useful. A bathtub can be modified with a cutout for accessibility, and restored when no longer needed. A motion-sensing nightlight is helpful to ensure a lighted path to the bathroom in the night.

The patient and caregiver should be instructed as to what to do in the case of falls. A patient can be trained to get up from the floor safely by pushing a chair to the wall and getting on all fours and pulling themselves up if there are no injuries. A medical alert bracelet can be used so an abnormal gait will not be misinterpreted in public.

For incontinence a condom catheter may be helpful with male patients. A bedside commode can reduce the risk of falls in the night. Good hygiene care is important when incontinence is present to preserve skin integrity.

Dementia may cause the patient to be unable to use a personal emergency response system when left alone. Safety when alone and in the community needs to be evaluated. The level of dementia often drives the care needs. An adult day program or housing with services may be considered if the patient wishes to remain in the community. The risk of wandering should be evaluated. If the patient is at risk for wandering, the family may want to consider registering the patient with the Alzheimer’s Association Safe Return Program. This program helps identify and reunite people with dementia with their loved ones. A calm approach and patient attitude are essential to de-escalate behaviors caused by dementia. Eating should be supervised to assure the patient is able to maintain nutrition.

Special attention should be paid to the caregiver of a patient with NPH. They need coaching in order to be realistic about what the patient is able to do. A backup plan should be established in case the caregiver becomes incapacitated. Education about the disease progression is helpful so that the caregiver has a good understanding of what is happening and realistic expectations of the treatment. Special attention should be paid during times of transition from the hospital or nursing home and home. Providers that specialize in memory care, as well as adult day programs, and/or caregiver support organizations can support caregivers. A family conference and future planning for care should be offered along with financial planning for the future care needs.