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

• 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.

• 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