Potential placebo effect in assessing idiopathic normal pressure hydrocephalus.

Although shunt placement constitutes the primary treatment for idiopathic normal pressure hydrocephalus (INPH), it has been challenging to decide which patients to refer for such an intervention. Procedures involving CSF removal, such as large-volume lumbar puncture (LP) and external lumbar drainage, are commonly used to predict a successful response to surgery, but their positive and negative predictive values have considerable shortcomings. The authors here report the case of a 76-year-old woman with possible INPH whose condition improved equally well after actual and sham large-volume LPs. The authors discuss the implications of this placebo response in the context of the diagnosis and management of INPH. The authors suggest that the clinical response to sham procedures for CSF removal might provide important information for better predicting which patient might respond to shunt surgery.