Overview
Normal Pressure Hydrocephalus (NPH)
1. Clinical Overview
Summary
Normal Pressure Hydrocephalus (NPH) is a potentially reversible cause of dementia characterised by the clinical triad of Gait Disturbance, Dementia (Cognitive Impairment), and Urinary Incontinence – remembered by the mnemonic "Wet, Wacky, and Wobbly". Imaging shows Ventricular Enlargement (Ventriculomegaly) that is out of proportion to cortical atrophy, and importantly, CSF pressure is within the normal range on lumbar puncture (Hence "Normal Pressure"). NPH is most common in older adults (>60 years) and can be Idiopathic (iNPH) or Secondary (Following SAH, Meningitis, Trauma). The key importance of recognising NPH is that it is treatable – CSF Shunting (VP Shunt) can significantly improve symptoms, particularly gait. Predictors of shunt response include: improvement after Large Volume Lumbar Puncture (CSF Tap Test), Gait disturbance as the predominant early symptom, and Shorter symptom duration. [1,2,3]
Clinical Pearls
"Wet, Wacky, Wobbly": Urinary Incontinence (Wet), Dementia (Wacky), Gait Disturbance (Wobbly).
"Gait First and Foremost": Gait disturbance is typically the earliest and most prominent symptom. Improvement in gait predicts shunt response.
"Magnetic Gait": Described as "feet stuck to the floor" – Wide-based, Short shuffling steps, Difficulty initiating walking.
"CSF Tap Test": Improvement in gait after removing 30-50ml CSF = Positive tap test = Predicts good shunt response.
2. Epidemiology
Demographics
| Factor | Notes |
|---|---|
| Age | >60 years. Peak 70-80 years. |
| Sex | Slight male predominance. |
| Prevalence | ~1-2% of dementia cases. Underdiagnosed. |
Types
| Type | Notes |
|---|---|
| Idiopathic NPH (iNPH) | No identifiable cause. Most common. Older adults. |
| Secondary NPH | Follows SAH, Meningitis, Trauma, Tumour, Prior neurosurgery – Impaired CSF absorption. |
3. Pathophysiology
CSF Dynamics
- CSF Production: ~500ml/day by choroid plexus.
- CSF Circulation: Flows from ventricles → Subarachnoid space → Arachnoid granulations → Venous sinuses.
- CSF Absorption: Primarily via arachnoid granulations into superior sagittal sinus.
Mechanism in NPH
- Impaired CSF Absorption: Reduced absorption at arachnoid granulations.
- Transmantle Pressure: Slight pressure gradient across brain parenchyma (Not detected by standard LP).
- Ventricular Enlargement: Ventricles expand.
- Periventricular Pressure: Pressure on surrounding structures → Fibres to legs (Corona radiata), Frontal lobes, Bladder control centres.
- Normal Opening Pressure: Despite ventriculomegaly, LP opening pressure is within normal limits (less than 20cmH2O).
Why "Normal Pressure"?
- CSF pressure is measured as normal on single LP.
- Abnormality is in CSF dynamics (Impaired absorption) rather than sustained elevated pressure.
- May have intermittent B-waves (Pressure fluctuations) on continuous monitoring.
4. Clinical Presentation
Classic Triad ("Wet, Wacky, Wobbly")
| Feature | Description |
|---|---|
| Gait Disturbance (Wobbly) | First and Most Prominent. Wide-based, Short shuffling steps, Difficulty initiating walking ("Magnetic gait" – Feet stuck to floor), Difficulty turning, Apraxic gait. Improves with walking aid. |
| Dementia/Cognitive Impairment (Wacky) | Subcortical dementia pattern. Psychomotor slowing. Impaired attention/Concentration. Executive dysfunction. Memory less affected (Unlike Alzheimer's). |
| Urinary Incontinence (Wet) | Initially urinary urgency/Frequency. Progresses to frank incontinence. Often develops later. Faecal incontinence rare. |
Symptom Onset Order
Differential Diagnosis
| Condition | Key Features |
|---|---|
| NPH | Gait disturbance prominent, Ventriculomegaly disproportionate to atrophy, Normal pressure CSF, Responds to shunt. |
| Alzheimer's Disease | Memory impairment early and prominent. Cortical atrophy on MRI. |
| Vascular Dementia | Vascular risk factors. Stepwise decline. White matter changes on MRI. |
| Parkinson's Disease | Tremor, Rigidity, Bradykinesia. Response to L-Dopa. |
| Lewy Body Dementia | Visual hallucinations, Fluctuating cognition, Parkinsonism. |
| Obstructive Hydrocephalus | Mass lesion, Raised ICP, Papilloedema. |
Gait first → Then Cognitive decline → Then Urinary symptoms.
Common presentation.
Full triad present in ~50-60%. May have only one or two features.
Common presentation.
5. Investigations
Imaging
| Modality | Findings |
|---|---|
| CT Head | Ventriculomegaly. May show periventricular hypodensity (Transependymal CSF leak). |
| MRI Brain | Gold Standard. Ventriculomegaly (Evans' Index >0.3). Callosal angle less than 90°. Periventricular T2/FLAIR hyperintensity. Disproportionately enlarged subarachnoid space hydrocephalus (DESH) pattern. Narrowed sulci at vertex. "Flow void" in aqueduct. |
Evans' Index
- Definition: Ratio of maximum width of frontal horns to maximum internal skull diameter.
- Normal: less than 0.3.
- NPH: >0.3 (Ventriculomegaly).
Callosal Angle
- Measured on coronal MRI at level of posterior commissure.
- Normal: >100°.
- NPH: less than 90° (Ventricles expand, Corpus callosum is compressed upwards).
CSF Studies
| Test | Notes |
|---|---|
| Lumbar Puncture (Opening Pressure) | Normal (less than 20 cmH2O). Essential to exclude raised ICP. |
| CSF Analysis | Normal (Rule out meningitis, SAH). |
Diagnostic/Prognostic Tests
| Test | Description | Significance |
|---|---|---|
| CSF Tap Test (Large Volume LP) | Remove 30-50ml CSF. Assess gait before and after (Timed walk, Steps taken). | Improvement in gait = Positive = Predicts good shunt response. Sensitivity ~50-60%. Negative tap test does NOT exclude shunt-responsive NPH. |
| Extended Lumbar Drainage (ELD) | Continuous CSF drainage via lumbar drain over 3-5 days. | More sensitive than tap test. Reserved for uncertain cases. |
| Infusion Study | CSF infused to test absorption resistance (Rout). | Raised resistance predicts shunt response. |
| CSF Flow Study (Phase-Contrast MRI) | Assess aqueductal CSF flow. | Hyperdynamic flow may support diagnosis. |
6. Management
Management Algorithm
SUSPECTED NPH
(Gait disturbance, Dementia, Incontinence + Ventriculomegaly)
↓
IMAGING
- CT or MRI Brain
- Ventriculomegaly (Evans' Index >0.3)
- Disproportionate to atrophy
- Exclude mass lesion
↓
LUMBAR PUNCTURE
- Opening pressure (Exclude raised ICP)
- CSF analysis (Exclude infection/SAH)
↓
CSF TAP TEST (Large Volume LP)
- Remove 30-50ml CSF
- Assess gait before and 1-4 hours after
- Timed walk, Steps taken
┌────────────────┴────────────────┐
POSITIVE (Improved Gait) NEGATIVE (No Improvement)
↓ ↓
**SHUNT CANDIDATE** Consider Extended Lumbar Drain (ELD)
Refer to Neurosurgery OR Infusion Study
OR MDT discussion
↓
VP SHUNT INSERTION
(Ventriculoperitoneal Shunt)
- Adjustable valve preferred
- Monitor for complications
↓
POST-OPERATIVE FOLLOW-UP
- Gait assessment
- Cognitive testing
- Shunt review
Shunt Surgery
| Procedure | Notes |
|---|---|
| Ventriculoperitoneal (VP) Shunt | Most common. Catheter from lateral ventricle → Subcutaneous → Peritoneal cavity. |
| Ventriculoatrial (VA) Shunt | Alternative if peritoneal route not suitable. Into right atrium. |
| Lumboperitoneal (LP) Shunt | Less common. Lumbar subarachnoid space → Peritoneum. |
| Programmable Valve | Preferred. Allows non-invasive adjustment of drainage pressure. |
Expected Outcomes Post-Shunt
| Symptom | Response |
|---|---|
| Gait | Best response. ~70-90% improve. Often most dramatic. |
| Cognition | ~50-70% improve. Less predictable. |
| Incontinence | ~50-60% improve. May take longer. |
Predictors of Good Shunt Response
| Predictor | Notes |
|---|---|
| Positive Tap Test | Gait improvement after large volume LP. |
| Gait as Prominent/Early Symptom | Better than dementia-dominant. |
| Shorter Symptom Duration | less than 2 years = Better outcome. |
| Known Cause (Secondary NPH) | SAH, Trauma, Meningitis. |
| Less Severe Dementia | Better baseline cognition. |
7. Complications
Shunt Complications
| Complication | Notes |
|---|---|
| Shunt Infection | ~5-10%. Staph epidermidis. May need shunt removal and IV antibiotics. |
| Shunt Malfunction | Blockage (Proximal or distal), Disconnection. Symptoms recur. Requires revision. |
| Over-Drainage | Subdural haematoma / Hygroma. Low pressure headache. Adjust valve. |
| Under-Drainage | Symptoms persist. Adjust valve or revise shunt. |
| Seizures | Perioperative. |
8. Prognosis and Outcomes
| Factor | Notes |
|---|---|
| With Shunt | ~70-80% improve overall. Gait improves most. Quality of life improves. |
| Without Shunt | Progressive decline. Dementia worsens. |
| Early Intervention | Better outcomes. Don't delay referral. |
| Long-Term | May need shunt revisions. Lifelong follow-up. |
9. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| NPH | Japanese Guidelines (2012) | Diagnostic criteria. Tap test. Shunt indications. |
| Idiopathic NPH | International Guidelines (Relkin et al.) | Clinical, Imaging, Physiological criteria. |
Evidence Points
- CSF Tap Test: Predictive of shunt response but NOT 100% sensitive. Negative tap test doesn't rule out shunt-responsive NPH.
- Shunt Outcomes: Multiple studies show gait improvement in majority. Cognitive improvement less consistent.
10. Patient and Layperson Explanation
What is Normal Pressure Hydrocephalus?
NPH is a condition where fluid builds up inside the brain (In spaces called ventricles), but the pressure is not raised. This fluid buildup causes problems with walking, thinking, and bladder control.
What are the symptoms?
- Walking difficulties – Shuffling, Unsteady, Feels like feet are stuck to the floor.
- Thinking problems – Slowed thinking, Forgetfulness, Difficulty concentrating.
- Bladder problems – Urgency, Accidents.
Not everyone has all three symptoms. Walking problems are usually first.
Why is it important?
NPH is one of the few causes of dementia that can be treated. If diagnosed early, treatment can improve symptoms.
What is the treatment?
- Testing: A "Tap Test" where we remove some fluid from the spine. If walking improves afterwards, it suggests a good response to treatment.
- Surgery (Shunt): A thin tube is placed to drain the extra fluid from the brain into the abdomen, where the body absorbs it. This can significantly improve symptoms, especially walking.
What is the outlook?
With treatment, about 7-8 out of 10 people see improvement, especially in walking. The sooner you are treated, the better the outcome.
11. References
Primary Sources
- Relkin N, et al. Diagnosing idiopathic normal-pressure hydrocephalus. Neurosurgery. 2005;57(3 Suppl):S4-16. PMID: 16160425.
- Williams MA, et al. Diagnosis and management of idiopathic normal-pressure hydrocephalus. Neurol Clin Pract. 2013;3(5):375-385. PMID: 24175148.
- Ishikawa M, et al. Guidelines for Management of Idiopathic Normal Pressure Hydrocephalus (Second Edition). Neurol Med Chir (Tokyo). 2012;52(11):775-809. PMID: 23183074.
12. Examination Focus
Common Exam Questions
- Classic Triad: "What is the triad of Normal Pressure Hydrocephalus?"
- Answer: Gait Disturbance, Dementia, Urinary Incontinence ("Wet, Wacky, Wobbly").
- Earliest Symptom: "Which symptom typically presents first?"
- Answer: Gait Disturbance.
- Diagnostic Test: "What is the CSF Tap Test?"
- Answer: Large volume LP (30-50ml removed). Improvement in gait = Positive = Predicts good shunt response.
- Treatment: "What is the definitive treatment for NPH?"
- Answer: Ventriculoperitoneal (VP) Shunt.
Viva Points
- Evans' Index >0.3: Indicates ventriculomegaly.
- Normal LP Opening Pressure: Despite ventriculomegaly. CSF dynamics are abnormal, not sustained high pressure.
- Negative Tap Test ≠ Exclude Shunt: Tap test sensitivity ~50-60%. Consider ELD or infusion study.
- Reversible Dementia: NPH is an important cause of treatable dementia. Don't miss it.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.