What are the evaluation and management strategies for Normal Pressure Hydrocephalus (NPH)?

Evaluation and Management of Normal Pressure Hydrocephalus (NPH)

Diagnostic Evaluation

MRI brain without IV contrast is the first-line imaging test for suspected NPH, showing ventriculomegaly out of proportion to cortical atrophy. 1

Clinical Features to Identify

• Classic triad (Hakim's triad):
  • Gait disturbance (earliest and most responsive symptom)
  • Urinary incontinence
  • Cognitive decline

Imaging Findings

• MRI brain findings suggestive of NPH:

  • Moderate to severe ventriculomegaly with rounded frontal horns
  • Marked enlargement of temporal horns and third ventricle
  • Absence of or only mild cortical atrophy
  • Evans index > 0.3 (ratio of maximal width of frontal horns to maximal width of inner skull)
  • Callosal angle < 90°
  • Evidence of altered brain water content
  • Aqueductal or fourth ventricle flow void 1

• CT head without contrast is an acceptable alternative if MRI is contraindicated, but less sensitive for detecting:

  • Transependymal CSF flow
  • Subtle ventriculomegaly 1

Supplementary Diagnostic Tests

After confirming radiological findings, perform:

1. CSF Drainage Tests:

   • Lumbar tap test: Remove 30-50 mL CSF and assess for clinical improvement
   • External lumbar drainage (ELD): More sensitive than tap test for predicting shunt response

2. CSF Dynamics Assessment:

   • Lumbar infusion test to evaluate CSF outflow resistance
   • Cine MRI showing increased ventricular flow rate (supportive finding) 1

Management Approach

First-Line Treatment

Ventriculoperitoneal shunting is the treatment of choice for confirmed NPH, with 70-90% of appropriately selected patients showing clinical improvement. 2

Surgical Management Options

1. Ventriculoperitoneal (VP) Shunt:

   • Standard treatment with programmable valve to adjust drainage
   • Complication rate: 10-20% (includes infection, hemorrhage, overdrainage) 3

2. Endoscopic Third Ventriculostomy (ETV):

   • Alternative when obstruction is present
   • Less effective for idiopathic NPH
   • Performed through burr holes 3

Post-Operative Care

• Close neurological assessment
• Follow-up imaging to evaluate ventricular size
• Valve pressure adjustments as needed 3

Complications of Shunting

• Infection: 5-10%
• Hemorrhage: 5-10%
• CSF leak: 5-10%
• Shunt malfunction or obstruction: 10-20%
• Overdrainage leading to subdural collections: 5-10% 3

Special Considerations

Differential Diagnosis

• Alzheimer's disease
• Vascular dementia
• Parkinson's disease
• Lewy body dementia
• Frontotemporal dementia 2, 4

Complicating Factors

• 75% of NPH patients also have another neurodegenerative disorder
• This complicates diagnosis and may affect treatment response 2

Prognostic Factors

• Early treatment improves outcomes
• Gait symptoms typically respond better than cognitive symptoms
• Presence of comorbid neurodegenerative disease may limit improvement 4

Management Algorithm

1. Initial Evaluation:

   • Assess for classic triad symptoms
   • Perform MRI brain without contrast (or CT if MRI contraindicated)

2. If imaging suggests NPH:

   • Perform CSF tap test or external lumbar drainage
   • Assess for clinical improvement after CSF removal

3. If positive response to CSF drainage:

   • Proceed with ventriculoperitoneal shunt placement
   • Use programmable valve to allow pressure adjustments

4. If equivocal response:

   • Consider extended external lumbar drainage (72 hours)
   • Perform additional testing (infusion studies, cine MRI)

5. Post-shunt monitoring:

   • Clinical assessment at 1,3,6, and 12 months
   • Imaging to confirm appropriate ventricular size
   • Valve pressure adjustments based on symptoms

NPH remains an important treatable cause of dementia and gait disturbance in the elderly, with proper diagnosis and timely intervention offering significant improvement in quality of life.