What is the workup for Normal Pressure Hydrocephalus (NPH)?

Workup for Normal Pressure Hydrocephalus (NPH)

CT head without contrast or MRI head without contrast is the first-line imaging test for suspected NPH, with MRI being preferred when available due to its superior visualization of key diagnostic features. 1

Initial Clinical Assessment

• Focus on identifying the classic clinical triad:

  • Gait disturbance (cardinal sign): shuffling, magnetic, or "glued to the floor" appearance 2
  • Cognitive impairment/dementia
  • Urinary incontinence (may progress from urgency/frequency to frank incontinence) 3

• Risk factors to document:

  • Advanced age
  • History of meningitis, subarachnoid hemorrhage, or head trauma
  • Hypertension and diabetes 2

Diagnostic Imaging

First-Line Imaging

• MRI head without IV contrast (preferred) or CT head without IV contrast 1

Key Imaging Findings

• Ventriculomegaly out of proportion to cortical atrophy
• Evans index > 0.3 (ratio of maximum width of frontal horns to maximum inner skull width)
• Additional MRI findings supporting NPH diagnosis:
  • Enlarged temporal horns
  • Callosal angle < 90°
  • Evidence of altered brain water content
  • Aqueductal or fourth ventricle flow void 1
  • Rounded frontal horns
  • Periventricular hyperintensities 4

Advanced Imaging (when initial findings are equivocal)

• Cine MRI to evaluate CSF flow dynamics
  • Hyperdynamic aqueductal CSF flow correlates with good shunt response 1, 4
• Phase-contrast MRI to measure aqueductal CSF stroke volume
  • Elevated stroke volume predicts excellent shunt responsiveness 4

Supplementary Testing

CSF Dynamics Testing

1. Large-volume lumbar tap test (LTT):

   • Remove 30-50 mL of CSF via lumbar puncture
   • Document opening pressure (typically normal or mildly elevated)
   • Assess for clinical improvement in gait and cognition post-tap 3

2. Extended lumbar drainage:

   • Consider if LTT results are equivocal
   • Continuous CSF drainage for 72 hours (approximately 150-200 mL/day)
   • Monitor for clinical improvement

3. Infusion studies:

   • Measures CSF outflow resistance
   • Higher resistance correlates with better shunt response

Functional Assessment

• Timed Up and Go test (pre and post CSF removal)
• Standardized gait assessment
• Cognitive testing (e.g., Mini-Mental State Examination)
• Urinary symptom assessment

Differential Diagnosis Considerations

• Vascular dementia
• Alzheimer's disease
• Parkinson's disease
• Other neurodegenerative disorders 5

Interpretation and Next Steps

• Patients with the complete clinical triad, supportive imaging findings, and positive response to CSF removal are most likely to benefit from shunting
• Approximately 70-90% of properly selected patients improve with shunt placement 5
• Consider neurosurgical consultation for patients with:
  • Progressive symptoms
  • Characteristic imaging findings
  • Positive response to CSF removal tests

Common Pitfalls to Avoid

• Failing to consider NPH in elderly patients with gait disturbance and cognitive decline
• Attributing symptoms solely to other neurodegenerative disorders without considering NPH
• Delaying diagnosis and treatment (early intervention improves outcomes) 6
• Neglecting to perform CSF removal tests when imaging is supportive but not definitive
• Missing comorbid neurodegenerative conditions (75% of NPH patients have concurrent neurodegenerative disorders) 5