Normal pressure hydrocephalus
Normal pressure hydrocephalus (NPH), also termed symptomatic hydrocephalus, occurs when there is an increase in intracranial pressure (ICP) due to an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain, which can cause ventriculomegaly. 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 ICP, therefore, are not usually elevated. Because of this equilibration, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness. (Though some studies have shown pressure elevations to occur only intermittently). However, the enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient. The classic triad of gait disturbance, urinary incontinence, and dementia or mental decline, was first described by Hakim and Adams in 1965.[1] NPH is often misdiagnosed as Parkinson's disease, Alzheimer's disease, or dementia, due to its chronic nature and nonspecific presenting symptoms [see below]. 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 granulations.
There are 2 types of normal pressure hydrocephalus: idiopathic and secondary. The term idiopathic means that it has no known cause. The secondary type of NPH can be due to a subarachnoid haemorrhage, head trauma, tumour, CNS infection, or a complication of cranial surgery.[2]
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.[3][4] This is in accordance with comparable findings stating that although normal pressure hydrocephalus can occur in both men and women of any age, it is found more often in the elderly population, with a peak onset generally in the sixth to seventh decades.[5]
Patients with dementia that are confined to a nursing home and may have undiagnosed NPH, can possibly become independent again once treated. So far only one study was able to evaluate the prevalence of NPH, both diagnosed and undiagnosed, among residents of assisted-living facilities, showing a prevalence in 9 to 14% of the residents.[6]
Clinical manifestations
NPH may exhibit a classic triad of clinical findings (known as the Adams triad or Hakim's triad) of urinary incontinence, gait disturbance, and dementia (commonly referred to as "wet, wobbly and wacky" or "weird walking water").
- Gait disturbance is typically the initial and most prominent 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 corticospinal motor fibers descending to the lumbosacral spinal cord. The gait disturbance can be classified as mild (cautious gait or difficulty with tandem gait), marked (evident difficulty walking or considerable unstable gait) or severe (unaided gait not possible)[7] In the early stages, most often this gait disturbance occurs in the form of unsteadiness and impaired balance, especially when encountering stairs and curbs. Weakness and tiredness of the legs may also be part of the complaint, although examination discloses no paresis or ataxia.[8] Often a mobility aid is used for added stability, once the patient has reached the mild to marked stage. Such aids may include a quad cane or wheeled walker. The patient's gait at the marked stage will often show a decrease in step height and foot-floor clearance, as well as a decrease in walking speed. This style is often referred to as a magnetic gait, in which the feet appear to be stuck to the walking surface, and is considered the characteristic gait disturbance of NPH. The gait may begin to mimic a Parkinsonian gait, with short shuffling steps and stooped, forward-leaning posture, but there is no rigidity or tremor. An increased tendency to fall backwards is also seen, and a broad-based gait may be employed by the patient in order to increase their base of support and thereby their stability. In the very late stages, the patient can progress from an inability to walk, to an inability to stand, sit, rise from a chair or turn over in bed; this advanced stage is referred to as "hydrocephalic astasia-abasia"[8]
- Dementia is predominantly frontal lobe in nature and of the subcortical type of dementia. It presents in the form of apathy, forgetfulness, inertia, inattention, decreased speed of complex information procession (also described as a dullness in thinking and actions), and disturbed manipulation of acquired knowledge, which is reflective of the loss of integrity of the frontal lobes.[5] Memory problems are usually a component of the overall problem and have been predominant in some cases, 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, and is found to be of the spastic hyperreflexic, increased-urgency type associated with decreased inhibition of bladder contractions and detrusor instability.[5] In the most severe cases, bladder hyperreflexia is associated with a lack of concern for micturition due to the severe frontal lobe cognitive impairment.[5] This is also known as "frontal lobe incontinence", where the patient becomes indifferent to their 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 CSF opening pressure is 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. On the contrary, 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.
- In some centers, External lumbar drainage has been shown to have the highest sensitivity and specificity with regards to predicting a successful outcome following surgery.[9]
- 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.[11] 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.[12]
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
- ^ Adams, R.D., Fisher, C.M., Haskim, S. et al. (1965). Symptomatic occult hydrocephalus with "normal" cerebrospinal fluid pressure. A treatable syndrome. New England Journal of Medicine, 273, 117-126.
- ^ National Institute of Neurological Disorders and Stroke. (2011, April 29). NINDS Normal Pressure Hydrocephalus Information Page. Retrieved from http://www.ninds.nih.gov/disorders/normal_pressure_hydrocephalus/normal_pressure_hydrocephalus.htm
- ^ Brean A, Eide PK. Prevalence of probable idiopathic normal pressure hydrocephalus in a Norwegian population. Acta Neurologica Scandinavica 2008
- ^ Tanaka N, Yamaguchi S, Ishikawa H, Ishii H, Meguro K. Prevalence of Possible Idiopathic Normal-Pressure Hydrocephalus in Japan: The Osaki-Tajiri Project. Neuroepidemiology 2009; 32: 171
- ^ a b c d Younger, D.S. (2005). Adult Normal Pressure Hydrocephalus. In Younger, D.S. (Ed.), Motor Disorders (2nd edition) (pp. 581-584). Philadelphia, PA: Lippincott Williams & Wilkins.
- ^ 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
- ^ Krauss, J.K., Faist, M., Schubert, M., Borremans, J.J., Lucking, C.H., & Berger, W. (2001). Evaluation of Gait in Normal Pressure Hydrocephalus Before and After Shunting. In R’uzicka, E., Hallett, M., & Jankovic, J. (Eds.), Gait Disorders (pp.301-309). Philadelphia, PA: Lippincott Williams & Wilkins.
- ^ a b Ropper, A.H. & Samuels, M.A. (2009). Adams and Victor’s Principles of Neurology (9th edition). New York, NY: McGraw-Hill Medical.
- ^ 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
- ^ 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
- ^ Shunting normal-pressure hydrocephalus: do the benefits outweigh the risks? A multicenter study and literature review.[1]
- ^ 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
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