The recently updated Japanese guidelines draw attention to a specific MRI pattern of disproportionately enlarged subarachnoid space hydrocephalus (DESH), believed to be pathognomonic of idiopathic normal pressure hydrocephalus (iNPH). This chapter discusses why establishing the diagnosis of NPH remains a challenge fifty years after its classic description. The original diagnosis of NPH relied upon the presence of mild dementia, gait, and urinary difficulties (Hakim's triad) seen in association with ventriculomegaly on pneumo-encephalogram. More sensitive cognitive evaluation of iNPH patients requires specific tests for the assessment of subcortical frontal lobe deficits such as the Rey Auditory Verbal Learning Test, Stroop test, Grooved Pegboard, Trail Making A and B Test, and digit span test. This diagnostic test provides information about cerebrospinal fluid (CSF) dynamics and predicts outcome. It consists in either removal of CSF accompanied by pre and post functional evaluation, or an infusion (bolus or continuous) test.

Several theories have been proposed to explain the pathophysiology of gait dysfunction in normal pressure hydrocephalus (NPH). The variety of potential targets includes midbrain compression or atrophy, cortical dysfunction, cortical-subcortical or intracortical circuit abnormalities, postural disturbance, dopamine signaling abnormalities, and regional cerebral blood flow (rCBF) depression. This chapter presents objective measures of gait dysfunction that have been used clinically, and highlights some of the major theories postulated to explain gait dysfunction in NPH. Gait dysfunction in NPH has characteristic features that include a slow pace, short stride length, wide stance, and low foot-floor elevation. Objective measures of gait can be used to quantify the pattern of walking and step-taking, focusing on walking speed, stride length, cadence, equilibrium, and posture. Recognition of cortical involvement in locomotion stems from multiple research efforts evaluating gait in healthy individuals and those with cognitive disturbances.