Normal Pressure Hydrocephalus: Diagnosis and Treatment
Direct Answer
MRI brain without IV contrast is the preferred initial diagnostic test, and CSF shunt surgery is the definitive treatment for properly selected NPH patients, who have an 80-90% chance of symptom improvement. 1, 2
Clinical Presentation: The Classic Triad
NPH presents with three cardinal features that typically evolve in a predictable sequence:
- Gait disturbance occurs first in approximately 70% of patients and is the most characteristic feature—the feet appear "glued to the floor" or "magnetic" with a hypokinetic pattern 1, 2, 3
- Cognitive impairment develops later, manifesting as frontal lobe dysfunction with psychomotor slowing, deficits in attention, working memory, verbal fluency, and executive function 1
- Urinary incontinence completes the triad, though it may present as urgency, frequency, or nocturia before frank incontinence develops 3
Critical pitfall: Patients typically present late in the disease course due to gradual symptom onset, but early recognition is crucial because symptoms are more reversible when caught early 4, 5
Diagnostic Workup
Initial Imaging
MRI brain without IV contrast is the gold standard initial test because it identifies multiple characteristic features simultaneously 1, 2, 4:
- Ventriculomegaly with disproportionately enlarged subarachnoid-space hydrocephalus (DESH)
- Narrowed posterior callosal angle (<90°)
- Effaced sulci at the vertex with widened sylvian fissures
- Periventricular white matter changes
- Critical finding: Cerebral aqueduct flow void on MRI 2, 4
- Enlarged temporal horns out of proportion to hippocampal atrophy
CT head without IV contrast is acceptable when MRI is contraindicated, though it provides less detailed information about flow dynamics and white matter changes 1, 4
Laboratory Evaluation
Obtain these tests to exclude reversible mimics of cognitive impairment 1, 4:
- Complete blood count
- Serum electrolytes, BUN, creatinine
- Fasting blood glucose
- Thyroid-stimulating hormone
- Vitamin B12 level
- Liver function tests
- Urinalysis
Predictive Testing for Surgical Candidacy
The high-volume lumbar puncture (tap test) has high positive predictive value for identifying shunt-responsive patients 2, 6:
- Remove 30-50 mL of CSF via lumbar puncture 3
- Assess gait, cognition, and urinary symptoms before and after drainage
- Clinical improvement within 24-72 hours strongly predicts shunt responsiveness
- Critical caveat: A negative tap test does NOT exclude the possibility of successful treatment—some patients still respond to shunting 5, 6
Alternative: Prolonged external lumbar drainage reliably identifies shunt-responsive patients when the tap test is equivocal 2
Advanced predictor: Elevated aqueductal CSF stroke volume on phase-contrast MRI demonstrates high positive predictive value for shunt responsiveness 2
Differential Diagnosis Considerations
Key Distinguishing Features
- Alzheimer disease: Progressive memory loss and cognitive decline WITHOUT early prominent gait disturbance or urinary symptoms 1
- Lewy body dementia: Visual hallucinations, Parkinsonian symptoms, and fluctuating cognition distinguish it from NPH 1
Critical Comorbidity Issue
20-57% of NPH patients have coexisting Alzheimer's disease or other neurodegenerative conditions, and approximately 75% of patients with NPH severe enough to require treatment have another neurodegenerative disorder 1, 4. This does NOT preclude treatment—any patient showing improvement after CSF drainage deserves therapeutic intervention 5
Treatment Approach
Definitive Management
CSF diversion through ventriculoperitoneal shunt surgery is the definitive treatment 1, 2:
- Properly selected patients using contemporary diagnostic tests have an 80-90% chance of responding to shunt surgery 1, 2
- All three symptoms (gait, cognition, urinary) can potentially improve 2
- Serious complication rate is approximately 6% 2
- Symptoms gradually improve over weeks to months post-shunt placement 3
Alternative surgical option: Endoscopic third ventriculostomy (ETV) may be considered in select cases 7
Patient Selection Algorithm
- Clinical triad present (especially gait disturbance as first/dominant symptom) → Proceed to imaging
- MRI shows characteristic NPH features → Proceed to tap test
- Positive tap test response → Strong surgical candidate (80-90% success rate)
- Negative tap test BUT strong clinical/imaging features → Consider prolonged external lumbar drainage or phase-contrast MRI
- Improvement with extended drainage → Proceed to shunt surgery
- Coexisting neurodegenerative disease present → Does NOT exclude surgery if CSF drainage shows benefit 5