Normal-pressure hydrocephalus

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

NPH should be considered when an older adult develops a progressive higher-level gait disorder with executive slowing and bladder urgency. Ask which domain began first and observe standing, initiation, stride length, foot clearance, turning and dual-task performance. Patients may describe their feet as stuck or magnetic, yet pyramidal weakness and sensory loss are not sufficient explanations. Cognitive change tends to be frontal-subcortical, including slowed processing, reduced attention, apathy and planning difficulty. Urinary urgency and frequency may progress to incontinence. The full triad is neither necessary early nor specific: Parkinson disease, vascular cognitive impairment, Alzheimer disease, cervical myelopathy, neuropathy, medication effects and urological disease frequently produce overlapping features.

MRI is preferred when feasible to define communicating ventriculomegaly and competing pathology. The Evans index compares maximal frontal-horn width with internal skull diameter; greater than 0.3 is a supportive marker, not a treatment decision. Disproportionately enlarged Sylvian fissures with tight high-convexity sulci, a reduced callosal angle and transependymal flow can support NPH, whereas generalised sulcal enlargement suggests atrophy. Review aqueduct, posterior fossa, infarcts, white-matter disease and subdural collections. 'Normal pressure' is historical: a single lumbar measurement can be within the usual range despite abnormal CSF dynamics, and some patients have intermittent pressure elevation.

Specialist selection asks whether CSF diversion is likely to improve function enough to justify surgery. Record baseline Timed Up and Go, 10-metre walk, step count and, where available, cognitive or continence measures. A high-volume lumbar tap with repeat testing over the service-defined interval can demonstrate reversible gait change. Extended lumbar drainage or infusion testing may be considered when the first test is negative or equivocal and suspicion remains; NICE notes that lumbar infusion testing has adequate safety and efficacy to support use with normal governance. Ventriculoperitoneal shunting is common, using programmable valves in many services. Improvement is greatest for gait, less predictable for cognition and bladder symptoms, and attenuated by comorbid neurodegeneration. Discuss haemorrhage, infection, overdrainage and subdural haematoma, blockage and revision before consent.

Key points

Idiopathic normal-pressure hydrocephalus is a chronic syndrome of gait dysfunction, cognitive impairment and urinary symptoms associated with communicating ventriculomegaly and potentially responsive to CSF diversion.
Gait impairment is usually earliest and most prominent: short shuffling steps, broad base, poor initiation, freezing and difficulty turning despite relatively preserved leg power.
Cognition often shows psychomotor slowing, reduced attention and executive dysfunction rather than the isolated early encoding failure typical of Alzheimer disease.
Urinary urgency and frequency generally precede incontinence; faecal incontinence is late and non-specific and should not be used to complete a textbook triad.
Ventriculomegaly alone is common with cerebral atrophy; imaging must assess whether ventricular enlargement is disproportionate and whether alternative structural disease exists.
An Evans index above 0.3 supports ventriculomegaly but is not diagnostic; callosal angle and disproportionately enlarged subarachnoid-space features can add specialist context.
Use timed gait measures before and after a large-volume lumbar tap or external drainage when selecting for shunt; subjective recollection is less reliable.
Failure to improve after one tap reduces confidence but does not absolutely exclude shunt responsiveness, particularly when phenotype and imaging are strong.
Ventriculoperitoneal shunting can improve gait most reliably, but infection, subdural collection, overdrainage, obstruction and revision risk require careful shared selection.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Idiopathic communicating hydrocephalus

Most suspected late-adult NPH has no single identified cause and reflects altered cerebrospinal-fluid dynamics in an ageing brain.

Secondary meningeal injury

Subarachnoid haemorrhage, meningitis, trauma and prior neurosurgery can impair cerebrospinal-fluid absorption and produce a similar communicating hydrocephalus syndrome.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Impaired cerebrospinal-fluid clearance
Reduced absorption or altered pulsatile flow gradually enlarges the communicating ventricular system without a sustained dramatic pressure rise.
2
Periventricular tissue distortion
Ventricular expansion stretches frontal-subcortical white matter and compresses periventricular pathways controlling gait, cognition and bladder function.
3
Network dysfunction and reduced perfusion
Mechanical strain and impaired local perfusion slow executive-motor processing, producing gait initiation failure before broader cognitive and urinary decline.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Higher-level gait disorder

Short steps, broad base, initiation failure, freezing and multistep turns with relatively preserved strength suggest a frontal gait network disorder.

Frontal cognitive profile

Psychomotor slowing, impaired divided attention, apathy and executive dysfunction fit NPH better than an isolated severe early amnestic syndrome.

Bladder progression

Urgency and increased frequency followed by loss of control supports the syndrome, although common urological and medicine causes still require assessment.

Disproportionate ventriculomegaly

Enlarged ventricles with tight high-convexity sulci or other supportive morphology is more persuasive than ventricular size considered without the surrounding subarachnoid spaces.

Competing parkinsonism

Prominent rest tremor, asymmetric rigidity, reduced arm swing and levodopa response point towards Parkinson disease, though comorbidity can complicate a gait-led NPH phenotype.

Acute hydrocephalus mismatchRed flag

Rapid headache, vomiting, drowsiness, papilloedema or focal change is not idiopathic NPH and requires emergency imaging for acute pressure or another intracranial event.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Observed and timed gait assessmentFirst step
Why
Characterise the gait syndrome and create objective baseline measures for drainage testing and postoperative review.
Interpretation and limitations
Use time, step count, turning and balance with the same aid and conditions; clinically meaningful change matters more than an unblinded impression.
02
MRI brain
Why
Assess ventriculomegaly, CSF pathways, supportive morphology and vascular, degenerative or obstructive alternatives.
Interpretation and limitations
Evans index above 0.3 and DESH-like features support but do not prove NPH; generalised atrophy can enlarge ventricles without shunt-responsive physiology.
03
Large-volume lumbar tap test
Why
Look for temporary objective improvement after removal of CSF in a patient being considered for shunting.
Interpretation and limitations
A clear gait improvement strengthens predicted response; a negative single test has imperfect sensitivity and should be interpreted by the specialist team.
04
External lumbar drainage or infusion study
Why
Refine CSF-dynamics assessment when tap response is equivocal but clinical and imaging evidence remains plausible.
Interpretation and limitations
These invasive tests require specialist governance, infection and bleeding precautions and agreed objective outcomes; they are not routine primary-care procedures.
05
Cognitive, bladder and mimic assessment
Why
Measure other domains and identify neurodegenerative, spinal, neuropathic, medication or urological contributions.
Interpretation and limitations
Comorbidity does not automatically rule out shunting, but it changes expected benefit and the consent discussion, particularly for cognition.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Cerebral atrophy

Ventricular enlargement proportional to widened cortical sulci suggests ex-vacuo change from neurodegeneration rather than pressure-responsive hydrocephalus.

Parkinson or vascular gait disorder

Rigidity, asymmetric bradykinesia, stroke deficits or extensive small-vessel disease may explain shuffling and executive slowing without NPH.

Cervical myelopathy

Brisk limbs, hand clumsiness and a sensory level support cord compression rather than a frontal gait disorder.

Urological disease

Prostate, infection and overactive bladder commonly cause urgency or incontinence and cannot complete an NPH diagnosis without the gait-led syndrome.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SuspectStart with gait, not the complete triadFirst stepProgressive initiation and turning difficulty occurs with cognitive slowing or urinary urgency.

1Observe gait directly and record onset order, falls, aids, parkinsonian signs, pyramidal features, sensation and spinal symptoms.
2Obtain collateral cognitive and bladder history, review medicines and screen common metabolic, urological and neurodegenerative alternatives.
3Arrange structural brain imaging and compare ventricular size with sulci and CSF pathways rather than reporting ventriculomegaly in isolation.
4Refer a coherent gait-led phenotype to a specialist hydrocephalus or neurosurgical pathway before disability becomes irreversible.

02SelectMeasure response to CSF drainageClinical and imaging findings make shunt-responsive NPH a reasonable possibility.

1Record standardised timed walking, steps, turns and selected cognition or continence measures immediately before the procedure.
2Perform a high-volume lumbar tap under the service protocol after reviewing anticoagulation, infection and procedural safety.
3Repeat the same objective tests at defined intervals and collect patient and carer observations without allowing subjective enthusiasm to replace measurement.
4Use extended drainage or infusion testing selectively when uncertainty remains, discussing imperfect negative predictive value and procedure risk.

03TreatBalance shunt benefit and complication riskThe multidisciplinary team judges that likely functional gain justifies CSF diversion.

1Explain that gait response is generally more predictable than cognitive recovery and that coexisting Alzheimer or vascular disease may limit outcomes.
2Complete surgical and anaesthetic assessment, anticoagulant planning and consent for infection, haemorrhage, overdrainage, subdural collection, obstruction and revision.
3Implant and programme the shunt through local neurosurgical practice, then compare postoperative function with the pre-drainage baseline.
4Provide urgent return advice for headache, drowsiness, fever, wound change, recurrent gait decline or focal symptoms suggesting complication or malfunction.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Falls and mobility dependence

Freezing, poor initiation and unstable turning cause fractures, fear, deconditioning and eventual loss of independent walking.

Progressive cognitive dependence

Executive slowing and attention failure impair medicines, finances and self-care, with mixed neurodegeneration often limiting reversibility.

Urinary incontinence and skin harm

Urgency progressing to incontinence causes infection, moisture injury, social restriction, carer burden and increasing personal-care dependence.

Shunt complications

Diversion can cause infection, obstruction, overdrainage, subdural collection and repeated revision, even when gait initially improves.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat the same timed gait and turning measures used at baseline after tap testing, shunt adjustment and surgery, recording aids and footwear.
Track falls, walking independence, bladder urgency, continence, processing speed and caregiver observations separately because domains improve at different rates.
After shunting monitor wound, temperature, headache pattern, cognition and focal neurology for infection, overdrainage, subdural collection or obstruction.
Review valve settings and imaging only through the specialist pathway; symptom-driven repeated adjustments without objective comparison can create harm.
Continue management of Parkinson disease, neuropathy, arthritis, vascular disease and dementia because a successful shunt does not remove coexisting disability.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Feet often lead

The gait disorder commonly predates marked dementia or incontinence, so waiting for all three textbook features can miss the most treatable phase.

Large ventricles need a reason

Atrophy pulls ventricles open while hydrocephalus expands them through CSF dynamics; the surrounding sulci and clinical pattern help separate these mechanisms.

Tap tests need numbers

A timed turn or walking speed before and after drainage is more reproducible than asking whether the patient feels a little steadier.

Negative is not absolute

One lumbar tap has limited sensitivity, so strong phenotype and imaging may justify more prolonged drainage or infusion assessment before rejecting surgery.

Comorbidity shapes consent

A patient can have both NPH and Alzheimer pathology; potential gait gain may remain worthwhile even when cognitive improvement is unlikely.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for severe dementia and frank incontinence before considering NPH in a patient with a characteristic progressive gait disorder.
02
Diagnosing the condition from an Evans index or a radiology phrase alone without demonstrating a compatible functional syndrome.
03
Calling one subjective good afternoon after lumbar puncture a positive test without standardised pre- and post-drainage gait measurement.
04
Excluding shunt responsiveness absolutely after one negative tap despite a persuasive phenotype and specialist imaging features.
05
Promising that shunting will reverse all cognition and continence rather than explaining domain-specific and comorbidity-limited outcomes.
06
Failing to safety-net fever, drowsiness, new headache or recurrent gait decline after shunt insertion as possible urgent complications.