Freezing Phenomenon, the Fifth Cardinal Sign of Parkinsonism

Freezing is a common motor disturbance in patients with parkinsonism (Giladi et al., 1992; Fahn, 1995; Giladi et al., 1997). It most frequently affects gait (Giladi et al., 1992) and speech (Ackermann et al., 1993); writing and brushing teeth (Barbeau, 1976) are less commonly affected. Freezing phenomenon refers to transient episodes, usually lasting seconds, in which the motor activity being attempted by an individual is halted. This motor blockade is best described in relation to gait as if the feet seem “glued” to the floor or in other motor acts as a “block” in the execution of a task. It is typical that during the freezing episode the patient exerts increased effort to overcome the block with voluntary increased muscle tone (Andrews, 1973), but the movements are ineffective. Freezing episodes are unrelated to any weakness, flaccidity or decreased muscle tone, and once freezing has cleared, the patient moves or performs the task at the usual pace (Fahn, 1995).