5-Minute Clinical Consult

Hydrocephalus, Normal Pressure

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Basics

Description

  • Normal pressure hydrocephalus (NPH) is a clinical triad of gait instability, incontinence, and dementia (mnemonic: wet, wobbly, wacky). Originally described by Hakim and Adams in 1965, it occurs rarely, but is potentially treatable.
  • 2 forms of the disorder: 1. Idiopathic; 2. Secondary (to traumatic brain injury, infection, mass lesions or aqueductal stenosis)
  • Absence of papilledema on clinical exam and normal CSF pressures at lumbar puncture

Geriatric Considerations
Idiopathic NPH primarily affects persons age >60 years and extremely rare before age 40.

Epidemiology


Incidence
  • No formal epidemiologic data exist regarding NPH because of the lack of consensus-derived diagnostic criteria. The natural history of untreated NPH has not been studied.
  • Idiopathic (iNPH) form primarily affects elderly; at least >40 years of age.
  • Secondary form can occur at any age.
  • Affects both genders equally.
Prevalence
  • 3.3/100,000 age 50–59 to 181.7/100,000 age 70–79 for iNPH (1)
  • Estimated to be a contributing factor in ~6% of all cases of dementia (2)

Risk Factors

  • Idiopathic risk is unknown (case reports suggest a possible genetic link, but unsubstantiated).
  • Secondary form is due to head trauma, subarachnoid hemorrhage, meningitis, or encephalitis.

Pathophysiology

  • This is a communicating hydrocephalus, a disorder of decreased CSF absorption (not overproduction). In iNPH, the leading theory suggests poor venous compliance impairs the subarachnoid granulations´ ability to maintain baseline removal of CSF. In secondary NPH, scarring is likely.
  • The result is a pressure gradient between the subarachnoid space and the ventricular system.
  • CSF production decreases in the face of an increased pressure set-point (but still in excess of the amount of CSF absorbed).
  • Elevated pressure distends ventricles and compresses the brain parenchyma.
  • As a result of compression, ischemic changes occur in the parenchymal vasculature with subsequent tissue damage and loss.

Etiology

  • Some believe that the idiopathic form is a result of persistently insufficient removal of CSF by immature subarachnoid granulations from childhood.
  • Secondary NPH may result from:
    • Subarachnoid hemorrhage
    • Head trauma
    • Resolved acute meningitis
    • Chronic meningitis (tuberculosis, syphilis)
    • Paget disease of the skull

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