Normal‐Pressure Hydrocephalus: Another Treatable “Dementia”: Part I
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VOLUME 27 • NUMBER 16
August 15, 2005
This article is the first of two parts.
Normal-pressure hydrocephalus (NPH) is encountered
most often in elderly persons. In this condition, cerebrospinal
fluid (CSF) buildup within the ventricles causes them to
enlarge, and a variety of clinical symptoms is seen, includ-
ing gait disturbance, urinary incontinence, and dementia.
Because NPH is treatable, it is considered to be a cause of
reversible dementia. However, NPH still is largely under-
and misdiagnosed, with the result that a significant num-
ber of patients who otherwise would have been able to
maintain a functional lifestyle end up in nursing homes.
The reported incidence ranges from 1% to 10%, with some
authors suggesting that as many as 6% of residents of nurs-
ing homes may have NPH. Misdiagnosis results from many
factors, including failure of clinicians to entertain NPH as
a diagnosis, even when patient exhibits all the typical signs
and symptoms; or requirement by clinicians that the patient
be a “textbook” case before entertaining the diagnosis. Often,
reluctance to make the diagnosis stems from concerns about
the morbidity of shunting in this patient population. How-
ever, as in many other clinical entities, it is crucial to keep
this diagnosis in mind and to realize that even patients who
have only some of the clinical or radiologic findings asso-
ciated with NPH may have NPH. These patients will
respond to shunting, and therefore they should not be
denied that option unless a thorough evaluation is per-
formed and NPH is excluded.
In 1965, Adams et al. described a small series of patients
with various neurological symptoms, ventricular enlarge-
ment, and “normal” CSF pressure as revealed by lumbar
puncture who improved in response to shunting. Because
of the normal CSF pressure, this syndrome was given the
name normal-pressure hydrocephalus. NPH was defined as a
syndrome of progressive dementia and unsteady gait, with
dilatation of the ventricular system and CSF pressure less
than 200 mm. Since that time, the syndrome has gained wide
recognition, and it now is considered an important element
of the differential diagnosis for dementia in elderly persons.
Some cases of NPH are idiopathic, whereas others are
secondary to an insult to the central nevous system. It is
thought that these injuries result in scarring of the sub-
arachnoid spaces or the arachnoid villi, leading, in turn, to
an extraventricular blockage of the CSF circulation or altered
CSF absorption, a process that would explain the increased
resistance to CSF absorption regularly found in NPH. With
aging, the brain tissue looses its stiffness and becomes more
compliant. As CSF outflow is reduced, the ventricles will
enlarge. The pressure rises, but to a mild degree, and because
Another Treatable “Dementia”: Part I
Ghassan K. Bejjani, M.D., and Maxim D. Hammer, M.D.
Learning Objectives: After reading this article, the participant should be able to:
1. Describe the clinical presentation of normal-pressure hydrocephalus (NPH).
2. Explain the physiopathology of NPH.
3. Describe the role of the various diagnostic modalities of NPH.
A BIWEEKLY PUBLICATION FOR CLINICAL NEUROSURGICAL
CONTINUING MEDICAL EDUCATION
Category: Neural hydrodynamics
Key Words: Hydrocephalus,Normal-pressure hydrocephalus, dementia,
Dr. Bejjani is Clinical Assistant Professor, Department of Neuro-
surgery, and Dr. Hammer is Assistant Professor, Department of
Neurology, University of Pittsburgh Medical Center, 200 Lothrop
Street, Pittsburgh, PA15213; E-mail: firstname.lastname@example.org.
Dr. Bejjani has disclosed that he receives grant/research support from
Codman. Dr. Hammer has disclosed that he is a member of the speak-
ers bureaus for Bristol-Myers Squibb and Boehringer-Ingelheim.
Wolters Kluwer Health has identified and resolved all faculty con-
flicts of interest regarding this educational activity.
of the high degree of compliance of the aging brain, pres-
sure stays within the normal range. It is thought that
although the CSF pressure as revealed by lumbar puncture
registers as “normal,” it is higher than expected in that par-
ticular patient population.
It also is thought that the progressive ventriculomegaly
characteristic of NPH may cause compression of structures
adjacent to the ventricles, resulting in the clinical manifesta-
tions of the disease. For example, pressure on the frontal lobes
and their interconnections may cause dementia and cogni-
tive dysfunction; pressure on the cortical center for bladder
and bowel control in the paracentral lobes may cause incon-
tinence; and pressure on the corticospinal “leg fibers” descend-
ing lateral to the ventricles may cause gait disturbance,
although a subcortical contribution may play a role early on.
Approximately 50% of cases of NPH are idiopathic, and
no specific etiology can be found. These cases are thought
to be secondary to aging of the arachnoid granulations,
which leads in turn to decreased CSF absorption. Insults
so minor that they were not noticed by the patient may
accelerate the process by causing inflammation and scar-
ing of the subarachnoid spaces and villi. Known etiologies
of NPH include trauma, subarachnoid hemorrhage, menin-
gitis, previous neurosurgical intervention, and irradiation.
The gait abnormality characteristic of NPH is the earli-
est and most common finding in patients with this syn-
drome. The gait disturbance is not uniform and can vary
from patient to patient. It may described as shuffling, mag-
netic or broad based. The steps are shortened in the shuf-
fling gait, while the patient has difficulty raising the legs in
the magnetic gait, and the base is widened in the broad
based gait. The first two patterns may be seen in combina-
tion. The patient has difficulty turning, and families some-
times report that the patient has a tendency to fall backward.
The gait disorder represents an alteration of the patient’s
ability to move smoothly rather than weakness or true
imbalance. Sometimes the gait is described as giving the
appearance that the patient has forgotten how to walk, and
it may be referred to as gait apraxia. Excessive activity of the
antigravity muscles occurs in NPH, and this activity may
prevent smooth gait progression. There is some similarity
between the gaits of NPH and Parkinson disease: short
stride, slow gait, and difficulty turning. However, in NPH,
there is no cogwheel rigidity, no resting tremor, and no
response to levodopa. In cerebellar ataxia, other findings
are encountered, such as dysarthria, gaze-evoked nystag-
mus, and appendicular dysmetria. The presence of gait
alteration in NPH is the most significant positive clinical
prognosticator, possibly because of its relative specificity
compared with the other cardinal symptoms.
Cognitive decline is gradual, usually causing executive
dysfunction early in the course of the disease, and it may
be difficult to recognize unless specific tests are performed.
These deficits may manifest as “psychomotor slowing,”
verbal dysfluency, and deficits in planning. Avariable degree
of abulia is manifested by loss of spontaneity and initiative,
which have been termed the “abulic traits.” These traits can
progress to severe akinetic mutism. Rarely, agitation, delu-
sions, and hallucination may be present. On formal men-
tal status testing, nonverbal performance is affected more
severely than verbal performance. True aphasia is not seen.
Behavioral disturbances such as agitation and symptoms
of depression may be encountered. Hypersomnia occurs in
as many as 40% of patients. Somnolence and cognitive
impairment are more likely to improve after shunting than
are abulia and behavioral disturbances.
The urinary disturbance of NPH ranges from urinary fre-
quency to urgency to incontinence in advanced cases. Uri-
nary disturbance also can take the form of inability to realize
the need to urinate, resembling the incontinence of frontal
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EDITOR: Ali F. Krisht, M.D.*
University of Arkansas for Medical Sciences
ASSISTANT EDITOR: Cargill Alleyne, Jr., M.D.*
Medical College of Georgia
PRODUCTION ASSISTANT: Ronalda Williams
Badih Adada, M.D.
Ossama Al-Mefty, M.D.
Rick Boop, M.D.
Evandro de Oliveira, M.D.
Allan Friedman, M.D.
Gerardo Guinto, M.D.
Douglas Kondziolka, M.D.
Jacques Morcos, M.D.
Tom Origitano, M.D.
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Kalmon Post, M.D.
Richard Rowe, M.D.
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M. Gazi Yas ¸argil, M.D.
* Dr.Krisht and Dr.Alleyne have disclosed
that they have no significant relationships with
or financial interests in any commercial orga-
nizations pertaining to this educational activity.
syndromes. The slow gait contributes by preventing the
patient with urgency from reaching the toilet on time. Uri-
nary incontinence is present in half of the patients and is
nonspecific, with only 33% predictive value for improve-
ment. The differential diagnosis in elderly patients includes
a variety of disorders, including benign prostate hypertro-
phy, pelvic relaxation, and cystitis. Fecal incontinence is
The differential diagnosis of NPH includes a variety of
diseases leading to senile dementia, including Alzheimer
disease, frontotemporal dementia (Pick disease), Lewy body
disease, Parkinson disease (Fig. 1), corticobasal ganglionic
degeneration (CBGD), multi-infarct dementia, and depres-
sion. In Alzheimer disease, the magnetic gait is not present
until the late stages of the disease. In vascular dementia,
extensive ischemic changes are seen on MRI. However, cere-
brovascular ischemic disease also predisposes patients to
NPH. It is important to remember that multiple patholo-
gies may co-exist in elderly patients. We have seen some
patients, although few in number, with a dual diagnosis of
NPH and dementia. It is important to keep that in mind
while discussing therapy with the patient and family.
Diagnosis of NPH is a challenge. Many studies have been
published regarding NPH and the predictive values of the
various diagnostic tests. However, the range of results
reported among studies is wide, and evidence-based rec-
ommendations are difficult to make.
CT and MRI. The primary complicating factor encoun-
tered by the radiologist is the fact that NPH occurs in elderly
people. In this patient population, brain atrophy leads to
ventricular enlargement (hydrocephalus ex vacuo) even in
patients without NPH. Therefore, radiologists have been
trying to pinpoint other features revealed by neuroimag-
ing modalities that will help to diagnose NPH.
On CT scans, these distinguishing features include
enlarged temporal horns, enlarged ventricles out of pro-
portion to sulcal enlargement and brain atrophy, and an
increased Evans ratio (the ratio of the frontal horns’ distance
to the width of skull, measured from the inner calvarial
table). This ratio may be increased with ex vacuo ventricu-
lomegaly caused by non-NPH dementias. The presence of
enlarged sulci has been used as an indicator of ex vacuo ven-
triculomegaly and as a negative prognosticator. However,
more than half of patients with atrophy will respond to
shunting. Periventricular lucency, thought to be an indica-
tor of transependymal resorption, has not been shown to
correlate consistently with successful shunting.
Other features that are sought on MRI include transependy-
mal resorption, periventricular hyperintensities on T2-
weighted MRI, lack of hippocampal atrophy (which is more
specific for Alzheimer disease), increased CSF flow through
the sylvian aqueduct, and turbulence of CSF flow through
the intracerebral channels and foramina.
However, no single criterion has been documented to be
reliable in making the diagnosis of NPH with CT or MRI. In
our practice, most patients with NPH have had reports stat-
ing that they have “ventricular enlargement within the nor-
mal range for that age group.” Occasionally, the radiologist
will add, “however, normal pressure hydrocephalus cannot
be ruled out, and clinical correlation is recommended.” This
lack of specific criteria puts the referring physician at a loss
in deciding whether to refer the patient to a specialist.
Cisternography. Cisternography is one of the main tests
traditionally used for diagnosing NPH. The technique relies
on findings of early and persistent ventricular reflux of
radionuclide injected in the lumbar subarachnoid space via
a spinal tap. It is thought that because of increased resis-
tance to CSF absorption through the arachnoid granula-
tions, the dye is not absorbed at the convexity as readily as
in the normal population or the population with cerebral
atrophy. Therefore, it will reflux early on into the ventric-
ular system, where it clears slowly.
Cisternography is far from accurate for making a diag-
nosis of NPH, however. A normal cisternogram does not
rule out NPH, and currently it is thought that this technique
is no more sensitive than clinical findings in diagnosing
NPH and predicting response to treatment.
Therapeutic Trial of Cerebrospinal Fluid Diversion
Atherapeutic trial of CSF diversion is thought to predict
response to shunting and the presence of NPH. Two pro-
cedures are used most commonly: lumbar puncture (LP)
and continuous lumbar drainage.
Lumbar puncture.When LPis chosen, it is performed on
an outpatient basis, and the patient is seen 1 to 2 weeks later.
The patient’s family usually reports that the symptoms
improved the same or the following day and then worsened
after 1 to 2 weeks, although the symptoms did not return to
the same degree of severity that was present before the LP
The central nervous system will replace the 20 to 30 mL
drained via the LP within an hour. On the other hand, the
puncture site in the dura will allow CSF to leak into the
epidural space for a few days. We ask our patients to main-
tain their usual activities after the LP, rather than putting
them on bed rest with the head of the bed flat for a few
hours. The latter step is requested routinely in LPs per-
formed for other purposes, to avoid post-LP headaches.
Alternatively, gait can be analyzed immediately pre- and
post-LP. In this method, the patient is asked to walk a fixed
distance, e.g., a 25-foot distance marked within the hallway
of an outpatient clinic. The patient is asked to walk from one
marker to another, turn around, and return. The total 50-foot
walk is timed and videotaped. The LP is then performed,
with the objective of draining at least 30 mLof CSF. The gait
test is repeated immediately. Improvement is expected either
immediately or within the first 2 days after the LP.
Continuous lumbar drainage. In continuous lumbar
drainage, the patient is admitted, an external lumbar drain
is placed, and CSF is drained during a 2- to 3-day period.
The patient is assessed for improved clinical findings after
the drainage period.
CSF drainage, especially prolonged CSF drainage, is
thought by some authors to be a more reliable way of diag-
nosing NPH, because it replicates shunting. One series by
Marmarou et al. demonstrated that CSF drainage was more
than 90% accurate in predicting response to shunting. How-
ever, these tests may not be conclusive in some patients with
long-standing hydrocephalus or aqueductal stenosis. Some
series have reported that some patients who do not respond
to external drainage will improve with shunting. For that
reason, some authors argue that the ultimate therapeutic
trial is shunting. Unfortunately, shunting is not an innocu-
ous procedure, and the risk/benefit ratio must be addressed.
During lumbar puncture, resistance to outflow also may
be measured. Although resistance to outflow usually is
increased in NPH, it does not correlate consistently with
response to shunting.
In some cases, the diagnosis of NPH is straightforward,
but in others, it is more subtle and requires a heightened
index of suspicion. One of the most common problems is
that clinicians seek the typical clinical triad and a radio-
logical report stating the presence of hydrocephalus before
investigating further. In our experience and that of others,
in numerous patients, only one of the clinical components
of the triad may predominate or be the only one present.
In addition, some recent work has showed that patients
with only gait disturbance or with dementia respond bet-
ter to shunting than those who have the complete triad, as
if early diagnosis of the syndrome carries a better progno-
sis. Other patients may have ventriculomegaly that is missed
by the radiologist or read as normal for their age group,
and some patients have ventricles that are not massively
enlarged. Because NPH is one of the few reversible causes
of dementia, and because of the major financial and social
implications of dementia, it is extremely rewarding to the
clinician to diagnose these occasionally challenging patients
and restore their quality of life.
In our practice, we recommend shunting for patients
who present with typical clinical and radiological findings
and no other concurrent diagnosis such as Parkinson dis-
ease. When the symptoms are not as typical or there are con-
founding issues, we recommend a therapeutic LP. If the
patient improves clinically in response to the LP, then a
shunt is placed. If the patient does not improve with a spinal
tap, but clinical suspicion is still strong, we recommend pro-
longed drainage via a lumbar drain.
Adams RD, Fisher CM, Hakim S et al: Symptomatic occult hydrocephalus
with “normal” cerebrospinal fluid pressure: a treatable syndrome. N Engl
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Boon AJ, Tans JT, Delwel EJ, et al: Dutch normal pressure hydrocephalus
study: prediction of outcome after shunting by resistance to outflow of
cerebrospinal fluid. J Neurosurg 87:687, 1997
Bradley WG, Whittemore AR, Watnabee AS, et al: Association of deep white
matter infarction with chronic communicating hydrocephalus: implica-
tions regarding the possible origin of normal-pressure hydrocephalus.
AJNR Am J Neuroradiol 12:31, 1991
Hebb AO, Cusimano MD: Idiopathic normal pressure hydrocephalus: a sys-
tematic review of diagnosis and outcome. Neurosurgery 49:1166, 2001
Marmarou A, Young HF, Aygok GA, et al: Diagnosis and management of
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Figure 1. MRI scan of a 78-year-old man who had a severe mag-
netic gait and was labeled as having Parkinson disease.He even-
tually became wheelchair-bound. A shunt was inserted, and the
patient was walking independently within 3 weeks.
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