Normal pressure hydrocephalus (NPH)
-
Adult-onset chronic communicating HCP
- Triad of
mental status and gait impairment with urinary incontinence, in the absence of
papilledema and normal opening pressure on lumbar puncture was first
described by
- No gender
preference
-
Idiopathic NPH occurs in elderly patients, usually 6th or 7th
decade
Clinical
presentation:
- Triad
(pnemonic “wet, wacky, wobbly”):
- Urinary incontinence (45-90%)
- may
initially only complain of urgency / frequency
- rarely may also have fecal incontinence
- Mental impairment (up to 80%)
- subcortical-like dementia
- slowing of verbal and motor responses (bradyphrenia)
- apathetic, forgetfulness, decreased
attention
- preservation of cortical
functions e.g. language
- frontal release signs may be
present (snout, glabellar tap, palmomental)
- Gait disturbance (up to 90%)
- “apraxic” or “magnetic” gait, inability to life legs as if
they are stuck to the floor
- often confused with Parkinsonism (eg vascular) since
patient’s may display balance difficulty, shortened stride length, difficulty
turning and paratonic rigidity but NPH more broad based, outward rotated feet
and diminished height of steps
- Early in
course strength is intact, reflexes are usually normal and Babinski’s absent
- later in course patient may
develop brisk reflexes, upgoing plantar responses and spastic paraparesis
- May have
drop attacks with brief LOC early in course (? secondary to ventricular
enlargement)
- Headache,
nausea, vomitting and papilledema are absent
Features
differentiating NPH from PD:
- Rigidity,
tremor, and slowing of rapid alternating movements less commonly observed in
NPH
- Apraxic
or magnetic gait in NPH, rather than shuffling, festinating gait in PD
- Lack of
response to levodopa in NPH
Etiology:
Primary /
Idiopathic (1/3)
Secondary
causes:
Trauma
Infection e.g meningitis
Mucopolysaccharidosis of the
meninges
Achondroplasia
Differential
diagnosis
Neurodegenerative
disorder
Alzheimer’s disease
Vascular Dementia (incl. Subcortical
Binswanger’s type, eg CADASIL)
Fronto-temporal dementia
Parkinson’s disease
PSP
MSA
Primary Progressive Freezing Gait disorder
Infection
Encephalitis, chronic meningitis (e.g.
listeria, fungal, TB, syphilis)
Metabolic
Encephalopathy
Neoplastic
Paraneoplastic encephalomyelitis
Occult mass lesion (frontal lobes)
Pathophysiology:
- Not
clearly elucidated
- Most
common theory is that the initial event is diminished CSF absorption by the
arachnoid villi. Obstruction of CSF outflow leads to transient high-pressure
hydrocephalus with subsequent ventricular enlargement. As the ventricles
enlarge, CSF pressure returns to normal.
- Symptoms
thought to occur secondary to displacement of
periventricular structures
Dementia – distortion of periventricular limbic and
subcortical structures
Incontinence and gait impairment – distortion of central
fibers of corona radiata
- Alternate
theories suggest impairments in blood flow and metabolism (substantiated by
imaging studies)
Investigations:
- Normal
opening pressure and CSF profile
- However,
prolonged monitoring of ICP has demonstrated episodic intracranial hypertension
in some patients
Imaging
- CT or MRI
demonstrates enlarged ventricles out of keeping with ex vacuo dilatation of
ventricles secondary to cortical atrophy
- often have associated transpendymal edema, particularly in
frontal and occipital regions
- often have associated subcortical ichemic changes or lacunar
infarcts
- “jet sign” - prominent flow void in the aqueduct and third
ventricle (dark aqueduct and third ventricle on a T2-weighted image whereas
remainder of CSF is bright)
Treatment:
Conservative / Supportive
Acetazolamide with or without
repeated lumbar punctures
- limited long term value
Ventriculoperitoneal shunting
-
Inevitably, a decision must be made as to whether a patient will benefit from
shunting
- There are
no randomized controlled trials of shunt placement
- No
clinical factor or test reliably identifies patients which will benefit from
shunting
- Shunting
is NOT a benign procedure and should not be undertaken without careful
consideration of the risks
- A recent
systematic review of 35 studies including 883 patients with idiopathic and
secondary NPH (Hebb and Cusimano) found that:
Outcome
from shunting:
- 59%
(24–100%) showed some improvement (various outcome measures)
- 29%
(10–100%) had a prolonged or significant improvement
- 38%
(5-100%) had a shunt complication, including stroke, hemorrhage, infection,
seizure, death
- 22%
(0–47%) required additional surgery
- 6%
(0–35%) had permanent neurological deficit or death
Prognosis:
Prognostic
factors most reliably associated with good outcome following shunting were:
- Presence of the complete triad of symptoms (gait and
mental impairment and urinary incontinence)
- Presence of a clearly identified etiology (i.e. secondary
NPH)
- Predominance of gait difficulties with mild or absent
cognitive impairment
- Clinical improvement after CSF removal (CSF tap test)
- Baseline assessment of neuropsychological function and
timed walking of fixed distance, followed by lumbar puncture removing 30-50 ml
of CSF and subsequent reassesssment of neuropsychological function and timed
walking
- Look for improvement in mental status and/or gait (reduced
time to walk a fixed distance, reduced gait apraxia, or reduced freezing of
gait)
-
Prognostic factors associated with a poor outcome after shunting were:
- Concurrent cerebrovascular disease
- Dementia as predominant symptom
- Absence of gait impairment or onset of gait impairment
after mental impairment
Ancillary
tests that may be helpful in identifying patients which will benefit from
shunting
- Prolonged
controlled CSF drainage with an external lumbar drain for 3-6 days was
predictive of good response to shunting in 2 small studies
- An
enlarged subcortical low-flow region (midbrain and basal ganglia) on SPECT
predicted a positive response to shunt surgery in 3 small studies
Ancillary
tests that were NOT found to be useful in predicting a response to shunting:
- The
following CT/MRI markers did NOT consistently predict positive outcome
after shunting:
- An Evans index of >0.50 on CT (ratio of maximum width
of the frontal horns to the maximum width of the inner table of the cranium)
- Lack or cortical atrophy or occluded sylvian fissures and
cortical sulci on CT or MRI
- Periventricular lucencies
- Isotope
cisternography
- Radiolabeled tracer is injected into CSF by LP and
absorption is monitored for 3 days
- Normal response - tracer fails to enter ventricles, moves
over convexity of brain and disappears from CSF in 12-24 h
- Communicating hydrocephalus - tracer appears in ventricles
early on and persists 48-72h with little or no flow over convexities
- Identifies patients with communicating hydrocephalus but
is NOT useful in identifying patients who will benefit from shunting
References
Bradley et
al. NICP
eMedicine
Bret et al.
JNNP 2002;73:9-12
Hebb and Cusimano. Neurosurgery 49:1166–1186, 2001
Last update: October 2004
Reviewed by: pending
review
Neurological
Medicine Pocketbook
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2003-2004 UWO Neurology Residents
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