The Predictive Value of the Tap-test in Normal Pressure Hydrocephalus

Normal pressure hydrocephalus (NPH) represents 1 to 12% of dementias. It is characterized by gait disturbance, progressive mental deterioration and urinary incontinence, associated with enlargement of the ventricular system and normal cerebrospinal fluid (CSF) pressure. In typical cases, gait disturbance is the first and most salient sign, followed by forgetfulness or mild dementia, psychomotor retardation, apathy and, later on, urinary urgency or incontinence. These cases present minor diagnostic difficulties and they are the most likely to improve after shunting. Differential diagnostic problems may, however, arise in some patients with atypical or incomplete clinical manifestations, as well as in patients with “subcortical” dementia such as Parkinson’s disease, progressive supranuclear palsy and Binswanger’s disease, which is the most common cause of the syndrome. In these cases, the results of computerized tomography (CT), magnetic resonance imaging (MRI) or radionuclide cisternography (RC) can be inconclusive or insufficient to establish a correct diagnosis and particularly to predict which patients will improve after shunting, hence the need to develop better methods for selecting patients to surgery.