Normal pressure hydrocephalus: Wikis

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Normal pressure hydrocephalus
Classification and external resources
ICD-10 G91.2
ICD-9 331.9, 331.5
DiseasesDB 9089
MedlinePlus 000752
eMedicine neuro/277 radio/479
MeSH D006850

Normal pressure hydrocephalus (NPH) is a chronic type of communicating hydrocephalus whereby the increase in intracranial pressure (ICP) due to accumulation of cerebrospinal fluid (CSF) becomes stable and that the formation of CSF equilibrates with absorption. The ICP gradually falls but still maintains a slightly elevated level and the CSF pressure reaches a high normal level of 150 to 200 mmH2O. Measurements of CSF, therefore, are not usually elevated. Because of this equilibration, patients do not exhibit the classic signs of increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness. (Though some studies have shown pressure elevations to occur only intermittently). However, patients do exhibit the classic triad of gait difficulties, urinary incontinence, and mental decline as first described by Hakim and Adams in 1965. It is often misdiagnosed as Parkinson's disease, Alzheimer's disease, and senility due to its chronic nature and its presenting symptoms [see below]. And, although the exact mechanism is unknown, normal-pressure hydrocephalus is thought to be a form of communicating hydrocephalus with impaired CSF reabsorption at the arachnoid villi.

There are 2 forms of normal pressure hydrocephalus. The secondary form which is due to subarachnoid haemorrhage, head injury, cranial surgery, or CNS infection and the idiopathic form where the cause is at present unknown.

Recent population-based studies have estimated the prevalence of NPH to be about 0.5% in those over 65 years old, with an incidence of about 5.5 patients per 100,000 of people per year[1] and [2].

Patients with dementia that are confined in a nursing home and have undiagnosed NPH may become again independent if treated. So far only one study was able to evaluate the prevalence of NPH, both diagnosed and undiagnosed, among residents of assisted-living facilities, that ranging between 9 to 14% of the residents [3].

Contents

Clinical manifestations

NPH may exhibit the classic triad (also known as Adam's triad) of urinary incontinence, gait disturbance, and dementia (commonly referred to as "wet, wobbly and wacky" or "weird walking water").

  • Gait disturbance and Ataxia is the first symptom of the triad and may be progressive, due to expansion of the ventricular system, particularly at the level of the lateral ventricles, leading to traction on the lumbosacral motor fibers that run in this region. Often, this takes on the form of unsteadiness and impaired balance, especially on stairs and curbs. Weakness and tiredness may also be part of the complaint, although this is very vague. NPH gait disturbance is often characterized as a "magnetic gait," in which feet appear to be stuck to the walking surface until wrested upward and forward at each step. The gait may mimic a Parkinsonian gait, with short shuffling steps and stooped, forward-leaning posture, but there is no rigidity or tremor. A broad-based gait may be employed by the patient in order to compensate for the ataxia.
  • Dementia is predominantly frontal lobe in nature, with apathy, dullness in thinking, and slight inattention. Memory problems are usually the main problem, which can lead to the misdiagnosis of Alzheimer's disease. However, in NPH there may be an obvious discrepancy between (often severely) impaired recall and intact or much less impaired recognition. The dementia is thought to result from traction on frontal and limbic fibers that also run in the periventricular region.
  • Urinary incontinence appears late in the illness, consisting of increased frequency and urgency. Ultimately, the patient may exhibit "frontal lobe incontinence," where he becomes indifferent to his recurrent urinary symptoms.

Diagnosis

Diagnosis of NPH is usually first led by a lumbar puncture, followed by the evaluation of clinical response to removal of CSF. This can be followed by a CT, MRI, and continuous external lumbar CSF drainage during 3 or 4 days.

  • Lumbar puncture is usually the first step in diagnosis and the opening pressure measured carefully. In most cases, CSF pressure is usually above 155 mmH2O. Clinical improvement after removal of CSF (30 mL or more) has a high predictive value for subsequent success with shunting. This is called the "lumbar tap test" or Miller Fisher test. A "negative" test has a very low predictive accuracy, as many patients may improve after a shunt in spite of lack of improvement after CSF removal.
  • Infusion test is a test with higher sensitivity and specificity than a lumbar puncture. The outflow conductance (Cout) of the cerebrospinal fluid (CSF) system is a parameter considered to be predictive in selection for hydrocephalus surgery. Cout can be determined through an infusion test.
  • External lumbar drainage has been shown to have the highest sensitivity and specificity with regards to predicting a succesful outcome following surgery[4].
  • CT scan may show enlarged ventricles without convolutional atrophy.

Treatment

NPH may be relieved by surgically implanting a ventriculoperitoneal shunt to drain excess cerebrospinal fluid to the abdomen where it is absorbed. Once the shunt is in place, the ventricles usually diminish in size in 3 to 4 days, regardless of the duration of the hydrocephalus. Even though the ventricular swelling diminishes, only 21% of patients show a marked improvement in symptoms. The most likely patients to show improvement are those that show only gait disturbance, mild or no incontinence, and mild dementia.[6] A more recent study (2004) found better outcomes, concluding that if patients with idiopathic normal pressure hydrocephalus are correctly identified, shunt insertion yielded beneficial outcomes in 86% of patients, in either gait disturbance (81%), improved continence (70%), or both. They also observed that measurements in the diagnostic clinical triad, the cortical sulci size, and periventricular lucencies were related to outcome. However, other factors such as age of the patient, symptom duration, dilation of ventricles, and the degree of presurgical dementia were unrelated to outcome.[7]

Shunts in Developing Countries

Since the cost of shunt systems, including the high cost of revisions, is beyond the reach of common people in developing countries, most of them die without ever receiving a shunt. Looking at this point, a study done by Dr. Benjamin C. Warf comparing different shunt systems and highlighting the role of a low cost shunt system in most of the developing countries. This study has been published in the Journal of Neurosurgery: Pediatrics May 2005 issue. It is about comparing the Chhabra shunt system from Surgiwear to those of the shunt systems from developed countries. The study was done in Uganda and the shunts were donated by International Federation for Spina Bifida and Hydrocephalus.

References

  1. ^ Brean A, Eide PK. Prevalence of probable idiopathic normal pressure hydrocephalus in a Norwegian population. Acta Neurologica Scandinavica 2008
  2. ^ Tanaka N, Yamaguchi S, Ishikawa H, Ishii H, Meguro K. Prevalence of Possible Idiopathic Normal-Pressure Hydrocephalus in Japan: The Osaki-Tajiri Project. Neuroepidemiology 2008; 32: 171
  3. ^ Marmarou A, Young HF, Aygok GA. Estimated incidence of normal-pressure hydrocephalus and shunt outcome in patients residing in assisted-living and extended-care facilities. And which demographic gets this most? Neurosurgical Focus 2007; 22: 1-8
  4. ^ The value of supplemental prognostic tests for the preoperative assessment of idiopathic normal-pressure hydrocephalus.Marmarou A, Bergsneider M, Klinge P, Relkin N, Black PM.Neurosurgery. 2005 Sep;57(3 Suppl):S17-28
  5. ^ Ongoing search for diagnostic biomarkers in idiopathic normal pressure hydrocephalus. Andrew Tarnaris, Ahmed K Toma, Neil D Kitchen, Laurence D Watkins. Biomarkers in Medicine, December 2009, Vol. 3, No. 6, Pages 787-805
  6. ^ Shunting normal-pressure hydrocephalus: do the benefits outweigh the risks? A multicenter study and literature review.[1]
  7. ^ Poca MA, Mataró M, Del Mar Matarín M, Arikan F, Junqué C, Sahuquillo J. Is the placement of shunts in patients with idiopathic normal-pressure hydrocephalus worth the risk? Results of a study based on continuous monitoring of intracranial pressure. J Neurosurg. 2004 May;100(5):855-66. PMID: 15137605

Blumenfeld, Hal. Neuroanatomy through Clinical Cases, 2002.

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