A slow, shuffling, narrow-based gait is one of the most characteristic features of PD (83). The parkinsonian gait reveals certain features that overlap with the gait disturbance associated with normal pressure hydrocephalus (84,85). In a study of 50 subjects older than 70 years, Sudarsky and Ronthal (86) established a principal cause of the gait disorder in all but seven subjects ("essential gait disorder"). They, but not others (87), suggested that this senile gait is related to normal pressure hydrocephalus. The gait and postural problems associated with PD probably result from a combination of bradykinesia, rigidity, loss of anticipatory proprioceptive reflexes, loss of protective reaction to a fall, gait and axial apraxia, ataxia, vestibular dysfunction, and orthostatic hypotension. When gait disorder, with or without freezing and postural instability, is the dominant motor dysfunction, "lower body" parkinsonism should be considered in the differential diagnosis (88). This syndrome is thought to represent a form of "vascular" parkinsonism associated with a multi-infarct state. Furthermore, gait disorder and postural instability are typically associated with PSP (89,90).
One of the most disabling symptoms of PD is freezing or motor blocks, a form of akinesia (91,92). The observation that some patients even with severe bradykine-sia have no freezing and other patients have a great deal of freezing but minimal or no bradykinesia suggests that the two signs have different pathophysiologies. Furthermore, that bradykinesia usually responds well to levodopa and freezing does not indicates that freezing may be a manifestation of a nondopaminergic disturbance. Freezing consists of a sudden, transient (a few seconds) inability to move. It typically causes "start hesitation" when initiating walking and the sudden inability to move the feet (as if "glued to the ground") when turning or walking through narrow passages (such as the door or the elevator), when crossing streets with heavy traffic, or when approaching a destination (target hesitation). Patients often learn a variety of tricks to overcome freezing, such as marching to command ("left, right, left, right"), visual cues such as stepping over objects (end of a walking stick, pavement stone, cracks in the floor, etc.), walking to music or metronome, shifting body weight, rocking movements, and others (88,93,94). When freezing occurs early in the course of the disease or is the predominant symptom, a diagnosis other than PD should be considered. Disorders associated with prominent freezing include PSP, multiple system atrophy (MSA), and vascular parkinsonism (88,95).
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