INPH and Parkinson disease: differentiation by levodopa response

Differentiating between Parkinson disease (PD) and idiopathic normal pressure hydrocephalus (INPH) can be challenging for the practicing clinician. Patients with undiagnosed PD but with incidental ventriculomegaly run the risk of being subjected to unnecessary shunt surgery. Taking a family history of PD and establishing the presence of motor symptoms (tremor, rigidity, bradykinesia) and nonmotor symptoms could help to differentiate between the two disorders. For patients with parkinsonian features, a dopamine challenge test to exclude the possibility of idiopathic PD might be beneficial. In this article, we highlight the difficulty of accurately differentiating INPH from PD as illustrated by three clinical cases of patients referred for shunt surgery.