Diagnosis and treatment of idiopathic normal pressure hydrocephalus.
First described by Hakim and Adams in 1965, idiopathic normal pressure hydrocephalus (INPH) is an enlargement of cerebral ventricles (Fig 1) without evidence of chronic increased intracranial pressure (ICP). INPH is associated with a triad of symptoms including gait disturbance, dementia, and urinary incontinence (Relkin, Marmarou, Klinge, Bergsneider, & Black, 2005).
[FIGURE 1 OMITTED]
In 2000, the costs of treating INPH exceeded $1 billion. There were 27,870 patients with INPH treated that year, and more than 8,000 new cases diagnosed (Fife, 2003). According to the U.S. Census Bureau, in 2002 there were nearly 60 million people aged 55 years or older living in the United States. Average life expectancy was 77.2 years in 2001, according to the National Center for Health Statistics, Centers for Disease Control and Prevention. Average life expectancy is expected to continue to increase (CDC, 2003).
As people live well into their seventh decade and beyond, both the number of diagnosed cases of INPH and the associated treatment costs will increase. Understanding the symptoms, workup, diagnosis, and treatment of INPH is very important as this condition develops into a major public health issue. This article reviews INPH as a national healthcare issue and presents a case study.
EM, a 65-year-old man, presented with a profile of progressively worsening symptoms, including gait and balance impairment, deterioration of memory and cognition, and recent urinary urgency and incontinence. A family member brought him to his physician for evaluation and treatment. Although Mr. M's signs and symptoms could be attributed to the effects of aging, a careful and thorough evaluation was necessary to accurately diagnose his disorder.
Mr. M's evaluation included careful review of his medical history, as well as a thorough systems examination. Special attention was paid to any specific brain disease or brain trauma that could precipitate his presenting symptomology.
Any adult, especially one over 60 years of age that demonstrates an insidious onset of the triad of symptoms of gait disturbance, cognitive impairment, and urinary incontinence, should be evaluated by a geriatrician or internist, psychiatrist, neurologist, and neurosurgeon (Patwardan & Nanda, 2005). The characteristic profile of signs and symptoms in an older individual unexplained by any specific cause, along with a high degree of clinical suspicion by the physician, will focus the diagnosis towards INPH.
Many conditions affecting older individuals can mimic the symptom profile of INPH, including Parkinson's disease, Alzheimer's disease, metabolic and psychiatric disorders, endocrine dysfunction, infections, trauma, vascular and neurodegenerative disorders, and incontinence from urinary tract disorders (Relkin et al., 2005). These conditions must be ruled out as causes of Mr. M's symptoms before a diagnosis of INPH can be accurately made.
The diagnostic evaluation also includes lumbar puncture (LP) and brain imaging. Aging causes atrophy of brain tissue which can lead to ventriculomegaly. The degree of ventriculomegaly common in INPH is disproportionate to the amount of brain atrophy, and is measured via brain imaging. Atrophic changes in the older adult's brain may be imaged with computed tomography (CT) or magnetic resonance imaging (MRI). Either technique can identify the ventriculomegaly necessary for the diagnosis of INPH, but MRI can also identify other pathology responsible for symptoms similar to INPH (Fife, 2003).
The MRI scan in patients with INPH reveals dilated ventricles with preserved cerebral parenchyma, which is in contrast to the ventricular dilation and significant loss of brain tissue seen in patients with Alzheimer's disease. An MRI scan is also useful in identifying the amount of white matter changes around the ventricles. Although MRI is the most accurate diagnostic imaging modality, non-contrast CT remains the diagnostic imaging technique of choice for rapid and accurate diagnosis of hydrocephalus. The brain CT scan in INPH reveals enlargement of two lateral and third ventricles and relative sparing of the fourth ventricle. There is no single test or imaging study that can be used to conclusively diagnose INPH. It must be diagnosed clinically, because the symptoms caused by INPH overlap many other conditions that affect older adults (Aho & Karis, 2003). An LP may be performed to measure opening pressure of cerebrospinal fluid (CSF) and confirm that it is within the normal range (60-240 mm [H.sub.2]O; Relkin et al., 2005).
INPH typically occurs in adults more than 60 years old and is a progressive, chronic disorder without a specific identifiable cause. The classic triad of symptoms--gait disturbance, cognitive dysfunction, and urinary incontinence--generally responds to treatment if present for less than 2 years' duration. Gait and balance disturbances are often the first and most common symptom of INPH and may develop over the course of months or years (Relkin et al., 2005).
Produced at a rate of 20 ml per hour by the choroid plexus, CSF is located in all four ventricles. Fluid flows from the two lateral ventricles via the foramen of Monro into the third ventricle, then through the aqueduct of Sylvius into the fourth ventricle. It then exits via three small openings into the subarachnoid space where it circulates around the surface of the spinal cord and brain. CSF is reabsorbed by the arachnoid villi in the subarachnoid space into the cerebral venous system to maintain a constant volume and intracranial pressure within the brain. CSF functions to cushion and support the brain, and it plays an important role in brain metabolism. Approximately 140 ml of CSF is contained within the ventricles.
INPH is a disorder of CSF circulation, probably related to decreased absorption at the arachnoid villi leading to ventriculomegaly (Kernich, 2006). In INPH, CSF accumulation occurs in the ventricles, resulting in a temporarily elevated ICP. The increase in ICP causes ventricular dilation, which allows the ICP to reset at a higher pressure. This new sustained intracranial pressure, although within the normal range of 60-240 mm [H.sub.2]O, is higher than pressure prior to the onset of INPH (Relkin et al., 2005).
In INPH, as CSF gradually increases in volume, dilating the cerebral ventricles (Fig 1), brain tissue is compressed, acting as a temporizing mechanism to maintain ICP within a normal range. However, ventricular dilation exerts pressure on brain tissue deforming the white matter motor tracts and fibers directly adjacent to the lateral ventricles. Gait abnormalities result from compression of these white matter motor tracts and fibers; it is described as a "glue footed" or "shuffling" type of gait (Relkin et al., 2005). Cognitive disorders and urinary incontinence result from compression and deformation of adjacent motor tracts and fibers and white matter limbic structures (Agren-Wilsson, Eklund, Koskinen, Bergenheim, & Malm, 2005).
Mr. M's CT scan revealed dilation of both lateral ventricles and the third ventricle, with sparing of the fourth ventricle, findings commonly associated with INPH. According to expert opinion, unless the circulation of CSF is obstructed, which it is not in INPH, the fourth ventricle is relatively spared from dilation (Wilson & Islam, 2005). Based on the images and results of his comprehensive exam and workup, no specific cause for his symptoms was identified. Blood tests were performed to rule out other diseases and conditions that may cause similar symptoms, such as neurodegenerative disorders, cerebrovascular disease, urological disorders or other metabolic dysfunctions. With Mr. M's informed consent, the decision was made to perform an LP. An LP is done only when the clinician performing the procedure is certain that intracranial pressures are not elevated. Performing an LP when ICP is elevated can result in catastrophic brain stem herniation. Elevated ICP can be determined noninvasively by viewing the CT scan and assessing for the presence of papilledema; if present, then this finding is consistent with elevated ICP. Papilledema is a swollen and distorted optic disc with a characteristic reddish hue due to increased intracranial pressure transmitted through the subarachnoid space along the optic nerve (Hickey, 1997).
The physician and nurse review all pertinent lab studies, including a coagulation and immunity profile, prior to performing the LP. Coagulation studies will reveal any potential abnormalities in blood-clotting ability, which if present might require correction prior to doing an LP. An immunity profile, including complete blood count with differential, will reveal any evidence of an ongoing infection or immune incompetence that may be cause to postpone the LP.
Mr. M's LP showed an opening pressure of 160 mm [H.sub.2]O, which is less than the upper limit of the normal range of 240 mm [H.sub.2]O, and within the range of 105-190 mm [H.sub.2]O consistent with a diagnosis of probable INPH. Higher opening pressures correlate with the probability of INPH according to expert opinion (Marmarou, Bergsneider, Klinge, Relkin, & Black, 2005). Mr. M's ICP measurement is associated with his signs and symptoms, including his ventriculomegaly evident on CT. Based on his symptoms, evaluation, imaging studies, and LP results, Mr. M was diagnosed with INPH.
The next step in treating Mr. M was to attempt to determine his responsiveness to ventriculoperitoneal (VP) shunting (Fig 2). Although VP shunting is prone to complications and not appropriate for every patient with INPH, it remains the most commonly recommended therapy for INPH for patients who demonstrate a favorable risk to benefit ratio (Bergsneider, Black, Klinge, Marmarou, & Relkin, 2005). A study by Malm et al. (1995) found that the number of patients with INPH who improved from surgical management with a VP shunt declined from 64% at 3 months to 26% at 3 years. The study also found that a VP shunt may provide only temporary improvement lasting from 1 to 3 years. However, shunting can make a substantial difference in quality of life for many of these patients (Klinge, Marmarou, Bergsneider, Relkin, & Black, 2005).
[FIGURE 2 OMITTED]
The deterioration that affects shunt recipients over time suggests that VP shunts do not always halt the progression of INPH. As other comorbidities independent of INPH worsen, shunted individuals can experience overall deterioration. Therefore, every effort should be invested in attempting to predict the probability of shunt responsiveness in each patient prior to surgical implantation. Currently there is no widely accepted approach to predicting positive outcome following VP shunt placement in individuals with INPH. Shunting can result in dramatic symptom improvement in many patients, but only partial alleviation in others. Improvement rates following VP shunt placement are dependent on careful patient selection based on diagnostic and clinical findings. Patients who respond best to VP shunting are those with the typical clinical triad of dementia, urinary incontinence, and, most importantly, gait disturbance supported by diagnostic CT results. Overall improvement rates across several studies ranged between 30% and 96% (Klinge et al., 2005).
Although no single diagnostic criterion exists to diagnose INPH, or to predict a positive response to VP shunting, a high-volume lumbar tap of 30-50 ml of CSF can be useful as a predictor of shunt responsiveness prior to VP shunt surgery. A positive response to removal of 30-50 ml of CSF, assessed by measuring improvements in gait stability and urinary control, is a positive prognostic indicator for VP shunting. However, because INPH is responsible for less than 1% of all dementias, improvement in mental status as a result of VP shunting may be minimal (Miele, Bendok, Bloomfield, Ondra, & Bailes, 2004). A study by Kahlon et al. (2002) looked at 47 patients who received VP shunts because of positive response with symptomatic improvement from a high-volume LP. Of that group, 96% of shunt recipients reported subjective improvement. They concluded that VP shunt surgery can be based on a positive response to the high-volume LP tap test (Fife, 2003).
Important considerations when determining appropriateness for VP shunting include predicting shunt-responsive INPH, degree of surgical risk, including the individual's ability to tolerate anesthesia, and the severity of comorbidities. The neurosurgeon will also investigate the condition of the patient's abdominal cavity. A history of adhesions or peritonitis and previous abdominal procedures will be evaluated, and may exclude the patient from VP shunting. The surgeon must estimate abdominal back pressure in the peritoneal cavity that will receive CSF drainage, because underdrainage may occur due to absorption incompetence (Christiansen, 2002). Proper VP shunt function is dependent on the pressure differences between the ICP and abdominal cavity. Pressure in the abdominal cavity is normally lower than ICP so that CSF will flow into the abdomen. Any decrease in CSF flow into the peritoneal cavity must be investigated, focusing on conditions within the abdomen. Consideration must be given to the effects of obesity, constipation, small bowel obstruction, or ileus. If present, correction of any condition resulting in increased abdominal back pressure must be resolved to allow proper CSF diversion via the VP shunt (Bergsneider et al., 2005).
There are many shunt-related complications and risks that make proper patient selection an even more important challenge. Intracerebral hemorrhage, or bleeding along the tract of the shunt, is the primary procedure-related risk. A retrospective study revealed that of 36 patients treated with a VP shunt, there was a 3% incidence of intracerebral hemorrhage (Bergsneider et al., 2005).
Other complications include infection, with staphylococcus responsible for 90% of all shunt infections. Seizures, shunt obstruction, subdural fluid collections causing increased ICP, and headaches due to overdrainage can occur. The most serious complication of VP shunting is overdrainage of CSF resulting in stress and tension on cerebral vasculature, which causes a potentially lethal subdural hematoma. Incidence of the complications is listed in Table 1.
Prior to the high-volume LP, Mr. M was carefully evaluated for gait, cognition, and memory. Then between 30 and 50 ml of CSF was removed and he was reevaluated several hours later using the same pretap parameters. Improvement in symptoms several hours after the LP substantiates the diagnosis of INPH, and is a valuable predictor of positive shunt responsiveness. In a study by Mori (2001) of patients who underwent this test, 80% who showed symptom improvement following high-volume tap had a positive response to shunting at 3 months and 73% reported benefit at 3 years.
Prolonged lumbar drainage for 3-5 days with an indwelling catheter is another option to both accurately diagnose INPH and determine positive shunt responsiveness. During prolonged lumbar drainage, the patient's condition is carefully monitored. Studies have shown that this diagnostic method, despite the risks associated with it, actually proved even more predictive of the positive response to VP shunting than did the high-volume LP.
Results of studies by Chen et al. (1994) and Haan et al. (1988) demonstrated 100% success in predicting positive VP shunt responsiveness after 5 days of continuous CSF drainage via lumbar drain (Marmarou et al., 2005).
According to McGirt et al. (2005), patients with gait disturbances as their primary and most debilirating symptom were twice as likely to respond to VP shunting than patients whose primary symptom was incontinence or dementia (Verrees & Selman, 2004). Overall success rates of VP shunting range from 33%-90%, which emphasizes the challenge and importance of careful patient selection (McGirt et al., 2005).
Once the decision to place a VP shunt has been made, valve selection is of vital importance. There are many valve designs available today. As of 1999 there were at least 127 commercially available valve devices with more than 450 pressure ranges and 2,000 assemblies. Management of INPH is best accomplished by using a valve-regulating shunting system, which is designed to prevent both underand overdrainage of CSF. A flow-limiting valve operates by limiting CSF drainage under normal pressure conditions, but will switch to allow a higher flow rate in response to increased ICP. However, despite all of the advances, overall success and survival of a first shunt implantation is about the same as what was reported 20 years ago. Hence, further research is necessary. To regulate CSF drainage, today's valves are programmable and have built in antisiphon devices to prevent sudden overdrainage associated with position changes. Antisiphon devices use gravity to assist in regulating shunt pressure which controls the programmable valve and amount of CSF drainage (Verrees & Selman, 2004).
Failure to divert CSF from the ventricles through the VP shunt may occur due to suboptimal placement or distal catheter malposition. Shunt obstruction may occur at either proximal or distal ends of the shunt tubing. Shunt migration may occur due to improperly securing the device during placement (McGirt et al., 2005). Shunt revision may be considered in any of these situations.
After Shunt Placement
EM responded positively to the high-volume LP and the decision was made by him, his family, and the neurosurgery team to proceed with VP shunting. Surgery was uncomplicated and Mr. M made an uneventful recovery; he was discharged home 5 days after surgery. Mr. M and his family were aware that gradual improvement in his preshunt symptoms was expected. He and his family were educated on symptoms related to shunt complications and how to manage them; they were given important phone numbers to call and a scheduled follow-up appointment. Three months later, he was noted to have improvement in his preshunt symptom profile.
Overall, outcome after shunting varies in patients with INPH. Careful preoperative evaluation and postoperative follow-up are recommended (Bergsneider et al., 2005). Comparing the triad of symptoms preshunt and at follow-up evaluations is useful in determining the success of VP shunting for the individual. More research is needed both in determining who will benefit from VP shunting and on improving valve function in this growing national health issue.
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Questions or comments about this article may be directed to Vincent Vacca, MSN RN CCRN, at email@example.com. He is a clinical nurse educator in the neuroscience ICU at Brigham and Women's Hospital, Boston, MA.
Table 1. Incidence of Ventriculoperitoneal Shunt-Related Complications Incidence Complications (N=42) Study Subdural fluid collection 2%-17% Malm, Kristensen, Stegmayr, Fagerlund, & Koskinen (2000) Infections 3%-7.2% Malm et al. (2000) Patwardan and Nanda (2005) Postoperative seizures 3%-11% Malm et al. (2000) Mechanical failure or obstruction 40.7% Patwardan and Nanda (2005)
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|Publication:||Journal of Neuroscience Nursing|
|Article Type:||Clinical report|
|Date:||Apr 1, 2007|
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