Hydrocephalus, Normal Pressure
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- Normal pressure hydrocephalus (NPH) is a clinical triad of gait instability, incontinence, and dementia (mnemonic: wet, wobbly, wacky). Originally described by Hakim in 1957, it occurs rarely but is potentially treatable.
- Two forms of the disorder: idiopathic and secondary (to trauma)
- Absence of papilledema on clinical exam and normal CSF pressures at lumbar puncture
Idiopathic NPH primarily affects persons >60 years; extremely rare before 40 years
- 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.
- Male = female
- 3.3/100,000 age 50 to 59 years to 11.7/100,000 age 70 to 79 years for iNPH and increases to upwards of 5.9% in those ≥80 years
- Estimated to be a contributing factor in 6% of all cases of dementia
Etiology and Pathophysiology
- Idiopathic form is a communicating hydrocephalus, a disorder of decreased CSF absorption (not overproduction). In iNPH, the leading theory suggests that 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 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.
- 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 the following:
- Head trauma (most common)
- Subarachnoid hemorrhage
- Resolved acute meningitis
- Chronic meningitis (tuberculosis, syphilis)
- Paget disease of the skull
- 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.