Communicating hydrocephalus with normal CSF pressure presenting as the triad of gait disturbance, urinary incontinence, and dementia.
Overview
A communicating hydrocephalus characterized by ventriculomegaly disproportionate to cortical atrophy, normal CSF opening pressure, and the clinical triad of gait disturbance, cognitive impairment, and urinary incontinence. May be idiopathic or secondary to prior subarachnoid hemorrhage, meningitis, head trauma, or radiation.
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Risk factors
- Advancing age (>60)
- History of subarachnoid hemorrhage, meningitis, or significant head trauma (secondary NPH)
- Vascular comorbidities — hypertension, diabetes, white matter disease
- Family history (rare familial forms)
Pathophysiology
Impaired CSF absorption at arachnoid granulations, possibly with altered CSF dynamics and reduced compliance, leads to ventricular enlargement. Stretched periventricular tracts, particularly the corona radiata and corpus callosum, impair frontal and motor function. Coexisting Alzheimer pathology is common and confounds outcomes.
Clinical presentation
Symptoms
- Gait disturbance — the earliest and most characteristic feature; magnetic, shuffling, broad-based, with difficulty initiating ('feet stuck to floor')
- Cognitive impairment — frontal-subcortical pattern: psychomotor slowing, executive dysfunction, apathy (memory relatively spared)
- Urinary urgency progressing to incontinence (urge-pattern, frontal-type)
- Falls
- Triad is rarely all present at first; gait typically appears first, incontinence and cognitive change later
Signs / physical exam
- Magnetic gait — small steps, reduced stride, en bloc turning, no festination
- Postural instability without overt parkinsonian rigidity
- Frontal release signs in some
- Bedside cognition: bradyphrenia, impaired attention/executive function, set-shifting deficits
Classic findings
Older adult with 'wet, wobbly, wacky' — gait, incontinence, and cognitive change — and ventriculomegaly on imaging.
Differential diagnosis
- Parkinson disease — Asymmetric tremor, bradykinesia, rigidity; responsive to levodopa; gait shuffling but normal stride width
- Vascular dementia — Stepwise decline, focal deficits, extensive white matter disease on MRI
- Alzheimer disease — Memory dominant, hippocampal atrophy disproportionate to ventricular size
- Lumbar spinal stenosis — Gait worsens with walking, improves with sitting/forward flexion; lower extremity pain
- B12 deficiency / subacute combined degeneration — Sensory ataxia, posterior column signs, low B12
- Frontal lobe tumor / subdural hematoma — Focal lesion or extra-axial collection on imaging
- Obstructive hydrocephalus — Ventriculomegaly with anatomic obstruction (aqueductal stenosis, tumor); elevated CSF pressure
Diagnostic workup
Diagnostic criteria
Probable iNPH (Relkin/Marmarou 2005): progressive gait disturbance + at least one additional triad feature + ventriculomegaly without obstruction + normal CSF opening pressure (5-18 cm H2O on LP).
Labs
- CBC, BMP, TSH, B12, RPR (reversible dementia screen)
- Urinalysis to exclude UTI as incontinence contributor
Imaging
- MRI brain — ventriculomegaly (Evans index >0.3) disproportionate to cortical atrophy, with effaced cortical sulci over the convexity and dilated Sylvian fissures (DESH pattern: disproportionately enlarged subarachnoid space hydrocephalus)
- No aqueductal obstruction (distinguishes from obstructive hydrocephalus)
- CSF flow void through aqueduct on MRI
- Large-volume lumbar puncture ('tap test') — remove 30-50 mL CSF; reassess gait and cognition before and ~1-24 h after
- Extended lumbar drainage trial (3 days, 10 mL/h) — higher sensitivity than single tap
Treatment
First-line
- Ventriculoperitoneal (VP) shunt — definitive therapy; programmable shunts allow pressure titration to reduce overdrainage
- Patient selection driven by tap test or lumbar drain trial response, severity of triad, comorbidities, and surgical risk
- Gait improvement is the most reliable post-shunt outcome; cognitive and continence response are less predictable
- Multidisciplinary preoperative evaluation: neurology, neurosurgery, physical therapy, neuropsychology
Pre-shunt evaluation
- Standardized gait assessment (timed up and go, 10-meter walk) before and after CSF removal
- Cognitive testing (MoCA, frontal assessment battery)
- Exclude or document comorbid Alzheimer pathology (CSF Aβ/tau, amyloid PET) — predicts more limited shunt response
Post-shunt management
- Adjust programmable valve pressure for symptom control vs overdrainage (subdural collections)
- Routine surveillance for shunt failure: recurrence of gait/cognitive symptoms
- Physical therapy and gait training to consolidate gains
Second-line / adjunct
- Acetazolamide and serial LPs — temporizing measures only; not durable
- Cognitive rehabilitation and behavioral strategies for residual deficits
Complications
- Shunt malfunction (mechanical or infectious) — re-presentation with declining gait
- Subdural hematoma from overdrainage (more common with non-programmable valves)
- Shunt infection (~5%, higher in early postoperative period)
- Persistent cognitive impairment if AD pathology coexists
- Falls, urinary tract infection, deconditioning
PANCE pearls
- Gait disturbance is the symptom most likely to improve with shunting; isolated dementia rarely responds.
- Evans index = maximal frontal horn width / maximal inner skull diameter on the same axial slice; >0.3 supports ventriculomegaly.
- Disproportionately enlarged subarachnoid space hydrocephalus (DESH) on coronal MRI is a strong imaging predictor of shunt response.
- Tap test high specificity but limited sensitivity — a negative tap test does not exclude shunt-responsive NPH.
- Coexisting Alzheimer pathology is the most common reason for limited shunt response — counsel families accordingly.
References
- Relkin 2005 — Relkin N et al. Diagnosing idiopathic normal-pressure hydrocephalus. Neurosurgery 2005;57(3 Suppl):S4-S16.
- International iNPH Guidelines — Nakajima M et al. Guidelines for management of idiopathic normal pressure hydrocephalus (third edition). Neurol Med Chir (Tokyo) 2021;61:63-97.
- AAN Practice Advisory — Halperin JJ et al. AAN practice guideline: Idiopathic normal pressure hydrocephalus: Response to shunting and predictors of response. Neurology 2015;85:2063-2071.
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