|
The Neuro Center's physician newsletter. Click here to go to Neurogram's home page, the University of Virginia Health System's Memory Disorders, Neurosurgery or Neuropsychology pages.
Normal Pressure Hydrocephalus:
A potentially reversible dementia
Idiopathic normal pressure hydrocephalus (NPH) is characterized by communicating hydrocephalus and a clinical presentation of gait disturbance, cognitive impairment, and urinary incontinence, most commonly affecting patients in their 60s or 70s(14). Patients with a known cause of hydrocephalus (e.g. intracranial hemorrhage, meningitis, traumatic brain injury, brain tumor, previous intracranial surgery, etc.) do not meet the criteria for idiopathic NPH, and their management differs according to their primary disease.
Clinical deterioration in NPH is probably due to slow, progressive impairment of the periventricular blood flow(30). NPH is commonly treated with implantation of a shunt to divert excess CSF from the ventricles into another body cavity such as the abdomen. Improvement has been shown in 30-50% of patients, depending on the series and how carefully the patients are selected(3,30,31). However, the procedure historically carries a complication rate of approximately 40%(28,30) of which 20% are severe(30). Morbidity typically results from over-drainage (resulting in subdural hematoma), seizures, infections, and other complications from multiple shunt revisions(15). Given the burden of dementia on patients, families, and society, it is extremely important that patients with a reversible dementia such as NPH are effectively treated. At the same time, it is just as important to avoid neurosurgical procedures on patients for whom the risks outweigh the benefits.
The recent development of a programmable valve for use in a CSF shunt has greatly increased neurosurgical flexibility of management of NPH (See Fig. 1). Pressure, expressed as millimeters of water (mm H2O), can now be adjusted according to patient-oriented criteria for recovery (e.g., gait improvement, urinary incontinence resolution, lessening cognitive dysfunction). Adjustments are made externally using a  "programmer," which is similar to the device used to adjust pacemakers. The main advantage of this technology is that it allows for "revisions" of pressure to be performed without another invasive surgery. The hope is that this technology will greatly reduce the complication rate(15) as pressure adjustments will no longer be as invasive to the brain.
Imaging in NPH
In classic NPH, a head CT shows a moderate to severe ventricular enlargement out of proportion to cerebral atrophy and includes ballooned frontal horns and enlarged temporal horns without evidence of hippocampal atrophy(30). However, discriminating hydrocephalus from large ventricles from atrophy can be a thorny issue for the neuro-radiologist. Hippocampal(8) and temporal lobe(19) atrophy measurements on MRI have also been proposed to aid in the discrimination of these two dementias, although these results have been debated.
Traditionally, neuroimaging criteria (e.g., change in ventricle size) were used for treatment decision-making in NPH, as opposed to patient-oriented measures such as formal gait analysis, neuropsychological testing (beyond the Mini Mental Status Exam) and careful questioning on urinary continence. However, ventricle size change is delayed following positive response to shunting, and the relationship to patient function is unknown. Therefore, neuroimaging changes are far less sensitive measures of change than quantifiable clinical patient information. In the same vein, changes in patients' clinical function without concomitant radiological change are very possible.
Gait Changes in NPH
Gait changes and postural imbalance are typically the first presenting symptom of NPH and the most likely to improve after a shunt(5,10,30). There is no classic gait pattern; the gait has been described as ataxic and wide-based, with some references to magnetic gait and postural instability and falls(11). Gait analysis has shown that specific distinguishing features in NPH are a broad-based gait pattern with outward rotated feet, and a diminished height of steps(26). These gait problems are rarely helped by levodopa therapy(30), which also aids in discrimination from Parkinson's disease.
Urinary Continence in NPH
True incontinence occurs only in the later stages of NPH but increased urinary urgency is almost always present(5). Urinary continence is thought to relate to stretching of the periventricular nerve fibers and partial loss of inhibition of bladder contractions, with no evidence of loss of bladder-sphincter control. The myth that continence is due to incontinence sans gêne only occurs in the most severe forms, when bladder hyperreflexia is associated with lack of concern for micturition related to significant frontal lobe dysfunction(20).
Depression in NPH
One under-recognized symptom common in the setting of NPH is the high rate of depression in this population(23). Formal screening for depression, using the Geriatric Depression Scale (GDS)(33), a reliable and valid measure of depressive symptoms in the elderly population(22) may be useful. There are as yet no treatment studies of depression in NPH, although there have been some case reports of successful pharmacologic treatment with antidepressants(23).
Predicting shunt benefit
The implantation of a shunt to control NPH involves a neurosurgical procedure, and the outcomes of this population are variable, calling into question the risk-benefit ratio(28). Consensus on the best predictor of benefit from the shunting procedure has not yet been reached(15,21). Measures of conductance to CSF outflow during ICP monitoring have been shown to have the highest prediction of benefit from shunting(21,29) but ICP monitoring is invasive and has its own complication rate which can interfere with the ability to predict shunt success. Auditory event-related potentials can help discriminate NPH from AD non-invasively, although this test is rarely available outside university settings(24).The most common procedure is the high-volume lumbar puncture (HVLP), but rarely has this included rigorous pre-and post-psychometric testing(32), and a negative test may not exclude improvement after shunt placement(29). Neuropsychological testing bears further investigation as a non-invasive method to improve prediction of shunt benefit.
Neuropsychological prediction of NPH outcome
The cognitive profile of NPH has similarities with other "sub-cortical" dementias including slowing of mental processing, difficulty in planning and mental shifting, and impaired memory(4). These patterns of cognitive impairment are different from "cortical" dementias such as Alzheimer's disease (AD). In AD, patients have an encoding deficit and associated impaired recognition, whereas in NPH or other subcortical phenomena, memory impairment per se is more rare; when it exists there is impaired delayed recall with normal recognition, indicating a retrieval, not an encoding deficit(12,30). Subcortical dementias are characterized by differences in complex attention tasks and executive functioning, as well has behavioral manifestations(17). NPH patients are also expected to have impaired attention and visual construction, which is unusual in AD(17).
These types of neurocognitive deficits in NPH are easily overlooked in a quick bedside exam(4). Many NPH patients have no obvious clinical evidence of dementia but still perform on more sensitive testing in the impaired range(5). Marked improvement in cognition after shunting in NPH is documented less frequently than that of a gait disorder(16,27), but it is possible that this is due to an under-recognition of subtle deficits in previous research.
Serial neuropsychological testing with NPH patients is useful to quantify subtle pre-operative deterioration or post-operative dysfunction or improvement(9,27). For example, Thomsen and colleagues(27) performed a study of 40 patients before and 12 months after shunting for NPH. Comparison of the preoperative and postoperative test results showed that cognitive functions improved in 16 patients, were unchanged in 19, and deteriorated in five. Neuropsychological assessment in NPH can be performed using a few, brief measures taking 20-30 minutes for the patient to complete, which are sentitive to degree of dementia and still allow the discrimination of a cortical (e.g., AD) from a subcortical syndrome (e.g., NPH(4)). Brief measures include the formal administration of the Mini-Mental Status Exam (MMSE)(6) and the Mattis Dementia Rating Scale (DRS)(18) coupled with a good assessment of baseline, premorbid IQ (e.g., the Barona Index(1)).
Utility of cortical biopsy
Approximately 10-30% of all patients who present with suspected NPH have AD, either as a separate diagnosis or co-morbid with NPH(25). Whether or not the presence of AD pathology on biopsy is a negative indicator for shunt benefit has been debated(7,25) and may depend on the stringency of the neuropathological criteria used(2,13). Presence of AD features on biopsy may help with post-surgical treatment and planning (e.g., use of a cholinesterase inhibitor).
NPH at UVa
Neurosurgeon Dr. Mark Shaffrey and Neuropsychologist Dr. Elana Farace have received a grant from the Commonwealth of Virginia, Virginia Center on Aging, to perform a study of the usefulness of neuropsychological testing in patients shunted for NPH, with verification by brain biopsy.
-
1. Barona A, Reynolds CR, Chastain R: A demographically based index of premorbid intelligence for the WAIS-R. Journal of Consulting and Clinical Psychology 52:885-887, 1984
2. Bech RA: Shunting effects in patients with idiopathic normal pressure hydrocephalus; correlation with cerebral and leptomeningeal biopsy findings. Acta Neurochirurgica 141:633-639, 1999
3. Black PM, Ojemann RG, Tzouras A: CSF shunts for dementia, incontinence, and gait disturbance. Clinical Neurosurgery 32:632-651, 1985
4. Cummings J: Introduction, in Cummings J (ed): Subcortical dementia. New York: Oxford University Press, 1990, pp 3-16
5. Fisher CM: Hydrocephalus as a cause of disturbances of gait in the elderly. Neurology 32:1358-1363, 1982
6. Folstein MF, Folstein SE, McHugh PR: "Mini-mental state". A practical method for grading the cognitive state of patients for the clinician. Journal of Psychiatric Research 12:189-198, 1975
7. Golomb J: Alzheimer's disease comorbidity in normal pressure hydrocephalus: prevalence and shunt response. Journal of Neurology, Neurosurgery & Psychiatry 68:778-781, 2000
8. Golomb J: Hippocampal atrophy correlates with severe cognitive impairment in elderly patients with suspected normal pressure hydrocephalus. Journal of Neurology, Neurosurgery & Psychiatry 57:590-593, 1994
9. Goodman M: Dementia reversal in post-shunt normal pressure hydrocephalus predicted by neuropsychological assessment. Journal of the American Geriatrics Society 49:685-686, 2001
10. Graff-Radford NR, Godersky JC, Jones MP: Variables predicting surgical outcome in symptomatic hydrocephalus in the elderly. Neurology 39:1601-1604, 1989
11. Haan J, Jansen EN, Oostrom J, et al: Falling spells in normal pressure hydrocephalus: a favourable prognostic sign? European Neurology 27:216-220, 1987
12. Helkala EL, Laulumaa V, Soininen H, et al: Recall and recognition memory in patients with Alzheimer's and Parkinson's diseases. Annals of Neurology 24:214-217, 1988
13. Khachaturian ZS: Diagnosis of Alzheimer's disease. Archives of Neurology 42:1097-1105, 1985
14. Krauss JK, Droste DW, Vach W, et al: Cerebrospinal fluid shunting in idiopathic normal-pressure hydrocephalus of the elderly: effect of periventricular and deep white matter lesions. Neurosurgery 39:292-299; discussion 299-300, 1996
15. Larsson A, Wikkelso C, Bilting M, et al: Clinical parameters in 74 consecutive patients shunt operated for normal pressure hydrocephalus. Acta Neurologica Scandinavica 84:475-482, 1991
16. Malm J, Kristensen B, Karlsson T, et al: The predictive value of cerebrospinal fluid dynamic tests in patients with th idiopathic adult hydrocephalus syndrome. Archives of Neurology 52:783-789, 1995
17. Maruff P, Currie J, Malone V, et al: Neuropsychological characterization of the AIDS dementia complex and rationalization of a test battery. Archives of Neurology 51:689-695, 1994
18. Mattis S: Mental status examination for organic mental syndrome in the elderly patient, in Bellak L, Karasu T (eds): Geriatric Psychiatry. New York: Grune & Stratton, 1976, pp 77-121
19. Mauri M: The role of morpho-volumetric and memory correlations in the diagnosis of early Alzheimer dementia. Journal of Neurology 245:525-530, 1998
20. Pickard J: Normal pressure hydrocephalus-- To shunt or not to shunt, in C W, J G (eds): Dilemma in the management of the neurological patient. Edinburgh: Churchill Livingstone, 1984, pp 207-214
21. Raftopoulos C, Deleval J, Chaskis C, et al: Cognitive recovery in idiopathic normal pressure hydrocephalus: a prospective study. Neurosurgery 35:397-404; discussion 404-395, 1994
22. Rapp SR, Parisi SA, Walsh DA, et al: Detecting depression in elderly medical inpatients. Journal of Consulting & Clinical Psychology 56:509-513, 1988
23. Rosen H, Swigar ME: Depression and normal pressure hydrocephalus. A dilemma in neuropsychiatric differential diagnosis. Journal of Nervous & Mental Disease 163:35-40, 1976
24. Savolainen S: Auditory event-related potentials differentiate patients with normal pressure hydrocephalus and patients with concomitant Alzheimer's disease verified by brain biopsy. NeuroReport 12:33-37, 2001
25. Savolainen S: Prevalence of Alzheimer's disease in patients investigated for presumed normal pressure hydrocephalus: a clinical and neuropathological study. Acta Neurochirurgica 141:849-853, 1999
26. Stolze H: Comparative analysis of the gait disorder of normal pressure hydrocephalus and Parkinson's disease. [see comments.]. Journal of Neurology, Neurosurgery & Psychiatry 70:289-297, 2001
27. Thomsen AM, Borgesen SE, Bruhn P, et al: Prognosis of dementia in normal-pressure hydrocephalus after a shunt operation. Annals of Neurology 20:304-310, 1986
28. Vanneste J, Augustijn P, Dirven C, et al: Shunting normal-pressure hydrocephalus: do the benefits outweigh the risks? A multicenter study and literature review. Neurology 42:54-59, 1992
29. Vanneste J, van Acker R: Normal pressure hydrocephalus: did publications alter management? Journal of Neurology, Neurosurgery & Psychiatry 53:564-568, 1990
30. Vanneste JA: Diagnosis and management of normal-pressure hydrocephalus. Journal of Neurology 247:5-14, 2000
31. Vassilouthis J: The syndrome of normal-pressure hydrocephalus. Journal of Neurosurgery 61:501-509, 1984
32. Wikkelso C: Normal pressure hydrocephalus. Predictive value of the cerebrospinal fluid tap-test. Acta Neurologica Scandinavica 73:566-573, 1986
33. Yesavage J, Brink T, Rose T, et al: Development and validation of a geriatric depression screening scale: A preliminary report. Journal of Psychiatric Research 17:37-49, 1983 |