View as “PDF version”
Patient Safety Tip of the Week
Normal Pressure
Hydrocephalus: Unrealistic Expectations?
Sixty years ago, our mentors Raymond Adams
and C. Miller Fisher published a paper in the New England Journal of Medicine
identifying normal pressure hydrocephalus as a potentially treatable condition
(Adams1965).
After that publication there was a flurry of activity to identify patients who
might benefit from CSF shunting. But the number of patients who actually
improved after shunting was disappointing and some shunted patients developed
complications like subdural hematomas. This neurologist personally can only
count on one hand the number of my own patients who improved significantly after
shunting.
The clinical “triad” of normal pressure
hydrocephalus (NPH) is dementia, incontinence, and gait disturbance. The
syndrome is characterized by enlarged ventricles without obstruction to CSF
flow and “normal” CSF pressure on lumbar puncture. The concept is a good one.
The Law of Laplace states that wall tension in a spherical object or space is
proportional to the pressure and the radius of the sphere. So, even though the
CSF pressure measured by lumbar puncture is “normal”, the tension exerted on the
ventricular walls is elevated in the enlarged ventricles. Motor fibers from the
leg area of the cortex run most closely to the walls of the lateral ventricles,
providing a possible explanation for the gait disturbance. The gait
disturbance, though, is probably not due to leg weakness but rather is a gait
“apraxia” and may instead by related to pressure on frontal lobe structures.
Cortical projections related to the bladder also descend near the walls of the
lateral ventricles and pressure on them may explain the uninhibited neurogenic
bladder seen in NPH.
In clinical experience, those patients in
whom the gait disturbance is more prominent than the cognitive decline fare
best with shunting. In selecting patients for potential shunting, we use the
response to CSF drainage following lumbar puncture as an indicator of possible benefit.
Finally, a randomized controlled trial of ventriculoperitoneal
shunt surgery for NPH has been performed. Luciano et al. (Luciano
2025) conducted a
double-blind, randomized, placebo-controlled trial involving participants
selected for shunt surgery on the basis of gait-velocity improvement with
cerebrospinal fluid (CSF) drainage. Participants were randomly assigned to an
open-shunt valve setting or a placebo valve of a noninvasively adjustable
shunt. The primary outcome was the change in gait velocity 3 months after
surgery. Secondary outcomes were the change at 3 months in the Tinetti scale
total score (a measure of gait and balance, with lower scores indicating worse
gait and balance), Montreal Cognitive Assessment (MoCA) score (lower scores
indicate worse cognition), and Overactive Bladder Questionnaire score (higher
scores indicate worse urinary incontinence).
99 participants underwent randomization and
received the assigned intervention. At 3 months, gait velocity had increased in
the open-shunt group and was unchanged in the placebo group (treatment
difference of 0.21 m per second was statistically significant). 80% of the
participants in the open-shunt group had a change in gait velocity that
surpassed the substantial meaningful change threshold of 0.10 m per second in
older adults. A significantly greater improvement in the open-shunt group than
the placebo group was seen for the Tinetti scale score but not the MoCA score
or the Overactive Bladder Questionnaire score.
Regarding adverse events, the most serious
adverse events in the trial were two parenchymal hemorrhages at the time of
surgery, one of which ultimately resulted in death (that was in the placebo
group), and three subdural hematomas that resulted in treatment. More
participants in the open-shunt group had subdural bleeding (12% vs. 2%) and
positional headaches (59% vs. 28%). However, three subdural hematomas and three
hygromas were treated with noninvasive adjustment of the shunt valve setting.
Similarly, low-pressure headaches were treated by adjustment of the shunt valve
setting. An equal percentage had cerebral bleeding (2% in both groups). More
participants in the placebo group reported falls (46% vs. 24%), but the number
of participants with clinically significant falls was low and did not differ
substantially between groups (2 in the open-shunt group and 3 in the placebo
group).
The authors concluded that ventriculoperitoneal
shunting resulted in significant improvements at 3 months in gait velocity and
a measure of gait and balance but not in measures of cognition or incontinence.
Perhaps the biggest limitation of the trial
is that the follow up to date has only been 3 months. The authors plan to
continue evaluating patients for at least 12 months. That should provide an
answer to the sustainability of the gait improvement and perhaps indicate
whether there is any further change in cognitive performance of bladder
symptoms.
With any medical intervention we weigh the
potential benefits vs the potential risks. While this clinical trial
demonstrates ventriculoperitoneal shunting resulted in significant improvements
in gait, there were risks as well. And the question of sustainability remains
unanswered. Perhaps most importantly, it tells us that we must be circumspect
in what we tell our patients about expectations for cognitive function.
Improvement in gait is definitely an important goal, but many patients and
their families agree to the surgery in hopes that there will be a cognitive
benefit as well.
The accompanying editorial by our colleague
and good friend Allan Ropper (Ropper
2025) notes that the results
of the trial affirm the existence of idiopathic normal-pressure hydrocephalus
as a clinical entity and show that CSF drainage is usually effective. He points
out that the results are a signature advance given that no truly equivalent
trials have been performed. But he also cautions that the durability of the
effect of shunting on gait and any effect on cognition need to be evaluated at
12 months.
We applaud the investigators for undertaking
this much needed clinical trial and anxiously await their 12-month follow up.
While we traditionally include NPH as a “treatable”
cause of cognitive decline, it is important that we and our patients and their
families have realistic expectations when we consider ventriculoperitoneal shunting
References:
Adams RD, Fisher CM, Hakim S, Ojemann RG, Sweet WH. Symptomatic occult hydrocephalus with
“normal” cerebrospinal-fluid pressure — a treatable syndrome. N Engl J Med
1965; 273(3): 117-126
https://www.nejm.org/doi/10.1056/NEJM196507152730301
Luciano MG, Williams MA, Hamilton MG, et al.
A randomized trial of shunting for idiopathic normal-pressure hydrocephalus. N
Engl J Med 2025; Published September 16, 2025
https://www.nejm.org/doi/full/10.1056/NEJMe2511690
Ropper AH. Small Steps, Big Ventricles:
Idiopathic Normal-Pressure Hydrocephalus. N Engl J Med 2025; Published
September 16, 2025
https://www.nejm.org/doi/full/10.1056/NEJMe2511690
Print “PDF version”
http://www.patientsafetysolutions.com/