What is the best approach for diagnosing normal pressure hydrocephalus (NPH)?

Diagnosis of Normal Pressure Hydrocephalus

The best approach for diagnosing normal pressure hydrocephalus (NPH) includes brain imaging with MRI or CT without contrast, followed by CSF testing through a tap test or lumbar drainage to confirm the diagnosis and predict shunt responsiveness. 1

Clinical Presentation

NPH is characterized by a clinical triad:

• Gait disturbance: Usually the earliest and most prominent symptom
• Cognitive impairment: May be subtle initially
• Urinary incontinence: Often develops later in the disease course 2, 3

Not all patients present with the complete triad, with 25-50% showing atypical or incomplete manifestations 2.

Diagnostic Algorithm

Step 1: Brain Imaging

• First-line imaging: MRI head without IV contrast or CT head without IV contrast 1

• MRI findings suggestive of NPH:

  • Ventricular enlargement not entirely attributable to cerebral atrophy (Evans index >0.3)
  • Rounded frontal horns
  • Marked enlargement of temporal horns and third ventricle
  • Absence of or only mild cortical atrophy
  • Callosal angle <90°
  • Evidence of altered brain water content
  • Aqueductal or fourth ventricle flow void 1

• CT findings:

  • Ventriculomegaly out of proportion to sulci
  • Possible transependymal CSF flow 1

Step 2: CSF Testing

After imaging suggests NPH, proceed with CSF testing to:

1. Measure opening pressure (typically normal or mildly elevated)
2. Evaluate response to CSF removal

CSF testing options:

• CSF tap test (CSF-TT): Removal of 30-50 mL of CSF with assessment of gait and cognitive function before and after

  • A positive test strongly predicts shunt response
  • A negative test does NOT exclude potential benefit from shunting (low sensitivity) 2, 4

• Repeated CSF tap test (RTT): Multiple lumbar punctures over several days

  • Higher sensitivity than single tap test 2

• Continuous lumbar external drainage (LED): Placement of temporary lumbar drain for 2-3 days

  • Higher sensitivity than tap test 2, 4

Step 3: Additional Testing (if diagnosis remains unclear)

• Intracranial pressure (ICP) monitoring: Presence of B-waves during >50% of recording time supports diagnosis 4
• Lumbar infusion test: Evaluates CSF absorption capacity 5
• Cine MRI: Shows increased ventricular flow rate 1

Differential Diagnosis

NPH must be distinguished from:

• Alzheimer's disease
• Vascular dementia
• Parkinson's disease
• Other causes of gait disorders and dementia 6

Importantly, approximately 75% of patients with NPH also have another neurodegenerative disorder, complicating diagnosis 6.

Predictors of Shunt Response

The most reliable predictors of positive surgical outcome are:

• Positive response to CSF removal (tap test or lumbar drainage)
• B-waves during >50% of ICP recording time 4
• Presence of all three clinical symptoms of the triad
• Short duration of symptoms
• No significant comorbidities 3

Common Pitfalls to Avoid

1. Relying solely on imaging: Brain imaging alone is insufficient for diagnosis; functional assessment with CSF removal is crucial
2. Excluding patients based on negative tap test: A single negative tap test has low sensitivity and should not exclude patients from further evaluation
3. Missing NPH diagnosis: Up to 80% of cases remain unrecognized and untreated 6
4. Overlooking comorbidities: Other neurodegenerative disorders frequently coexist with NPH
5. Delaying treatment: Early intervention leads to better outcomes 6, 3

NPH is a potentially treatable cause of cognitive decline and gait disturbance. The diagnostic approach should be thorough and systematic, with brain imaging followed by CSF testing to confirm the diagnosis and predict response to shunting.