What is Normal Pressure Hydrocephalus (NPH)?

Normal Pressure Hydrocephalus (NPH)

Normal Pressure Hydrocephalus is a clinical syndrome characterized by the triad of gait disturbance, urinary incontinence, and cognitive impairment, with ventriculomegaly on imaging and normal cerebrospinal fluid pressure on lumbar puncture, which is potentially reversible with CSF diversion through shunting. 1

Clinical Presentation

NPH presents with a characteristic clinical triad:

1. Gait disturbance - Usually the earliest and most prominent symptom

   • Shuffling, bradykinetic gait
   • Difficulty initiating steps
   • Wide-based stance
   • Increased risk of falls

2. Urinary incontinence - Typically develops after gait problems

   • Often presents as urgency initially
   • May progress to complete incontinence

3. Cognitive impairment - Usually occurs later in disease progression

   • Executive dysfunction
   • Psychomotor slowing
   • Memory impairment
   • Can progress to dementia if untreated

Pathophysiology

NPH involves:

• Initially raised CSF pressure followed by ventricular enlargement
• Decreased absorption of CSF at transcapillary or transvenular level
• Development of interstitial edema
• Ischemic damage to white matter
• Eventual normalization of CSF pressure despite persistent ventriculomegaly 1

Etiology

NPH can be classified as:

1. Idiopathic NPH - No identifiable cause, accounts for majority of cases

   • May be related to benign external hydrocephalus in infancy followed by deep white matter ischemia in adulthood 2

2. Secondary NPH - Results from:

   • Trauma
   • Intracranial hemorrhage
   • Meningitis (infectious or non-infectious)
   • Venous sinus thrombosis
   • Vasculitis 1

Diagnostic Evaluation

Imaging

• MRI brain (preferred):

  • Ventriculomegaly (enlarged lateral and third ventricles)
  • Narrowed posterior callosal angle
  • Effaced sulci along high convexities with widened sylvian fissures
  • Periventricular white matter changes
  • Cerebral aqueduct flow void 1

• CT head without contrast (alternative):

  • Can identify ventriculomegaly and other key findings
  • Less sensitive for periventricular white matter changes
  • Cannot detect cerebral aqueduct flow void 1

Diagnostic Testing

• Lumbar puncture with large-volume CSF tap:

  • Normal opening pressure (typically <20 mmHg)
  • Clinical improvement after CSF removal supports diagnosis
  • High positive predictive value for shunt response 3

• DTPA Cisternography:

  • Shows persistent radiotracer activity in lateral ventricles
  • Absence of radiotracer over cerebral convexities on delayed imaging
  • Insufficient evidence alone to determine shunt candidacy 1

Differential Diagnosis

NPH must be distinguished from:

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

Approximately 75% of NPH patients requiring treatment also have another neurodegenerative disorder, complicating diagnosis 4

Treatment

Surgical Management

• Ventriculoperitoneal shunt placement is the treatment of choice:
  • 70-90% of properly selected patients show clinical improvement 4
  • Improvement in gait typically occurs first, followed by urinary symptoms and cognition

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%) 5

Prognosis

• Without treatment, NPH typically progresses to nursing home dependence 4
• Early diagnosis and treatment significantly improve outcomes
• Patients with secondary NPH generally respond better to shunting than those with idiopathic NPH 2
• Patients with moderate to severe Alzheimer's disease burden are significantly less likely to respond to shunting 1

Key Points for Clinicians

• NPH is estimated to affect 3.7% of patients over 65 years of age 1
• It accounts for up to 10% of dementia cases and is one of the few potentially reversible causes 2
• Approximately 80% of cases remain unrecognized and untreated 4
• Early intervention with shunting offers the best chance for symptom improvement
• Close neurological assessment and follow-up imaging are essential after treatment 5

NPH should always be considered in elderly patients presenting with the characteristic triad of symptoms, as early diagnosis and treatment can significantly improve quality of life and prevent progression to disability.