What are the diagnostic and treatment approaches for normal pressure hydrocephalus (NPH)?

Normal Pressure Hydrocephalus: Diagnosis and Management

Normal Pressure Hydrocephalus (NPH) should be diagnosed through a combination of clinical assessment (gait disturbance, cognitive impairment, and urinary symptoms), brain imaging showing ventriculomegaly, and cerebrospinal fluid testing, with treatment via ventriculoperitoneal shunt placement being the most effective intervention for appropriately selected patients. 1

Diagnostic Approach

Clinical Presentation

• Classic Triad:
  • Gait disturbance: Wide-based, magnetic gait with short shuffling steps (typically the first and most prominent symptom)
  • Cognitive impairment: Slowed processing, attention deficits, executive dysfunction
  • Urinary symptoms: Progressing from urgency to frank incontinence 1

Imaging Studies

• MRI brain without contrast (preferred):

  • Ventriculomegaly out of proportion to cortical atrophy
  • Evan's index >0.3
  • Callosal angle <90 degrees
  • Enlargement of temporal horns
  • Evidence of altered brain water content
  • Aqueductal or fourth ventricle flow void 1

• CT head without contrast (if MRI contraindicated):

  • Ventriculomegaly
  • Transependymal CSF flow
  • Coronal reformations to assess hippocampal atrophy 1

CSF Studies

• Lumbar puncture with opening pressure measurement:
  • Normal or mildly elevated CSF pressure (70-245 mm H₂O)
  • Normal CSF composition 1

Predictive Testing for Shunt Response

CSF Tap Test

• Remove 30-50 mL of CSF via lumbar puncture
• Assess gait and cognitive function before and after tap
• Positive response suggests shunt responsiveness
• Low sensitivity (single tap) but high specificity 2

Extended Testing (for inconclusive cases)

• Repeated CSF tap test (RTT) or
• Continuous lumbar external drainage (LED) for 72 hours
• Intracranial pressure monitoring: Presence of B-waves during >50% of recording time strongly predicts positive shunt response 3

Supplementary Tests

• Radionuclide cisternography: May show delayed clearance of radiotracer over cerebral convexities (less commonly used now) 1
• CSF infusion tests: Can demonstrate CSF dynamics malfunction 3

Treatment Algorithm

1. Initial Evaluation:

   • Confirm clinical triad (complete or partial)
   • Verify ventriculomegaly on imaging
   • Rule out mimics and secondary causes

2. Predictive Testing:

   • Perform CSF tap test
   • If positive → proceed to shunt surgery
   • If negative/inconclusive → consider extended testing (RTT or LED)

3. Surgical Intervention:

   • Ventriculoperitoneal shunt placement is the treatment of choice 4
   • Programmable shunts allow pressure adjustments post-surgery
   • 70-90% of properly selected patients show clinical improvement 4, 2

4. Alternative Treatment:

   • For patients who cannot undergo shunt surgery due to high surgical risk:
     • Consider repeated lumbar punctures as maintenance therapy
     • Some patients maintain favorable outcomes for at least 1 year with this approach 5

Post-Treatment Monitoring

• Follow-up until symptoms resolve
• Monitor for shunt complications
• Urgent neuroimaging for:
  • Worsening symptoms despite treatment
  • New focal neurologic symptoms
  • Change in headache pattern 6

Pitfalls and Caveats

• 25-50% of NPH cases present with atypical or incomplete clinical manifestations 3
• Approximately 75% of NPH patients may have coexisting neurodegenerative disorders, complicating diagnosis 4
• A negative CSF tap test should not exclude patients from consideration for shunt surgery due to its low sensitivity 3
• Untreated NPH typically progresses to dependence on nursing care 4
• The benefit-to-risk ratio of shunt surgery is highly favorable when patients are properly selected 2

Differential Diagnosis

• Alzheimer's disease
• Vascular dementia
• Parkinson's disease
• Lewy body dementia
• Cervical myelopathy
• Lumbar spinal stenosis
• Other causes of gait disturbance and cognitive decline 7

Early diagnosis and treatment of NPH is crucial, as properly selected patients have an 80-90% chance of responding to shunt surgery, with potential improvement in all symptoms 2.