Normal Pressure Hydrocephalus: Diagnosis and Management
Diagnostic Approach
In an elderly patient presenting with progressive gait difficulty, urinary incontinence, and mild cognitive decline, obtain brain MRI to look for ventriculomegaly with disproportionately enlarged subarachnoid-space hydrocephalus (DESH), followed by a CSF tap test to confirm the diagnosis of idiopathic normal pressure hydrocephalus (iNPH). 1, 2
Clinical Presentation
The classic triad does not need to be complete for diagnosis 2:
- Gait disturbance typically appears first and is most severe, characterized by magnetic gait, shuffling, short steps, and wide-based walking 1, 3, 2
- Cognitive impairment manifests as slowed processing, impaired short-term memory, and difficulties with executive function 4, 5
- Urinary incontinence presents as urge incontinence rather than overflow 1, 4
Neuroimaging Requirements
MRI brain is the essential first-line investigation 1, 5:
- Look for ventriculomegaly (not from cerebral atrophy) with DESH pattern 1, 6
- Assess for transependymal edema 7
- Evaluate for closing of CSF space at high convexity 6
- Rule out secondary causes (prior hemorrhage, meningitis, trauma) 8
The DESH finding on MRI is now considered essential for imaging diagnosis and guides the decision for further management 1.
CSF Tap Test
The CSF tap test has high positive predictive value and is the key diagnostic tool 4, 5, 2:
- Remove 30-50 mL of CSF via lumbar puncture 5
- Measure opening pressure (typically normal: 70-245 mm H2O) 4, 9
- Assess both objective and subjective improvements in gait, cognition, and urinary symptoms within hours to days 2
- Use timed gait testing (Timed Up & Go test) before and after tap 10, 2
A negative tap test does NOT exclude the possibility of shunt-responsive NPH 4. If clinical suspicion remains high with supportive imaging, consider extended lumbar drainage or proceed to shunt trial 5.
Management Strategy
Surgical Treatment
Ventriculoperitoneal (VP) shunt placement is the definitive treatment for patients with positive tap test response 1, 9, 6:
- Use programmable valves to minimize overdrainage complications 6
- Expect significant improvement in gait (primary benefit), with variable improvement in cognition and urinary symptoms 10, 2
- Monitor for shunt complications including infection, malfunction, and subdural hematomas 1
Recent evidence shows endovascular shunting (eShunt) as an emerging minimally invasive alternative with low serious adverse event rates (3.0%) and significant symptom improvement at 90 days 10.
Prognostic Considerations
Patients with moderate to severe Alzheimer's disease burden are significantly less likely to respond to shunting 8. Co-pathology is common in elderly patients and must be considered when predicting outcomes 8.
Comorbid cervical stenosis is common and may require separate surgical intervention 2. Evaluate for this if gait improvement after tap test is incomplete.
Diagnostic Algorithm
Elderly patient with gait disturbance ± cognitive decline ± urinary incontinence → Obtain brain MRI 1, 5
MRI shows ventriculomegaly with DESH → Perform CSF tap test with pre/post gait assessment 1, 2
Positive tap test (objective gait improvement) → Refer to neurosurgery for VP shunt 1, 6
Negative tap test but high clinical suspicion → Consider extended lumbar drainage or neurosurgical consultation for shunt trial 5
MRI normal but high clinical suspicion → Reconsider differential diagnosis; NPH is unlikely 5
Common Pitfalls
- Do not dismiss the diagnosis if only one or two elements of the triad are present—gait disturbance alone with supportive imaging warrants evaluation 2
- Do not rely solely on CSF opening pressure—it is typically normal in NPH despite ventricular enlargement 4, 9
- Do not confuse ventricular enlargement from cerebral atrophy with true NPH—look specifically for DESH pattern 1, 6
- Screen for cognitive impairment using validated tools (Mini-Mental State Examination, Montreal Cognitive Assessment) to establish baseline and monitor response 11, 2