INPH typically occurs in adults more than 60 years old and is a progressive, chronic disorder without a specific identifiable cause.
INPH is a disorder of CSF circulation, probably related to decreased absorption at the arachnoid villi leading to ventriculomegaly (Kernich, 2006).
In INPH, as CSF gradually increases in volume, dilating the cerebral ventricles (Fig 1), brain tissue is compressed, acting as a temporizing mechanism to maintain ICP within a normal range.
M's CT scan revealed dilation of both lateral ventricles and the third ventricle, with sparing of the fourth ventricle, findings commonly associated with INPH.
Higher opening pressures correlate with the probability of INPH according to expert opinion (Marmarou, Bergsneider, Klinge, Relkin, & Black, 2005).
Although VP shunting is prone to complications and not appropriate for every patient with INPH, it remains the most commonly recommended therapy for INPH for patients who demonstrate a favorable risk to benefit ratio (Bergsneider, Black, Klinge, Marmarou, & Relkin, 2005).
As other comorbidities independent of INPH worsen, shunted individuals can experience overall deterioration.
However, because INPH is responsible for less than 1% of all dementias, improvement in mental status as a result of VP shunting may be minimal (Miele, Bendok, Bloomfield, Ondra, & Bailes, 2004).
Important considerations when determining appropriateness for VP shunting include predicting shunt-responsive INPH, degree of surgical risk, including the individual's ability to tolerate anesthesia, and the severity of comorbidities.
Improvement in symptoms several hours after the LP substantiates the diagnosis of INPH, and is a valuable predictor of positive shunt responsiveness.
Prolonged lumbar drainage for 3-5 days with an indwelling catheter is another option to both accurately diagnose INPH and determine positive shunt responsiveness.