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