Gait Disorders

Anatomy and Pathophysiology

Normal gait requires the integration and coordination of the central and peripheral nervous systems and the musculoskeletal system. Gait consists of two key components: (1) locomotion, the generation and maintenance of rhythmic stepping, and (2) equilibrium, the ability to keep the body upright and maintain balance. In quadrupedal animals, locomotion is mainly dependent on spinal pattern generators, which produce rhythmic stepping movements. In contrast, locomotion in primates can be elicited by electrical stimulation of brainstem areas, including the posterior subthalamus, dorsal and ventral portions of the caudal pons, and the mesencephalic tegmentum. The latter includes the pedunculopontine nucleus (PPN), a group of cholinergic neurons that receives input from the basal ganglia and motor cortex and projects to the spinal cord and reticular nuclei. Although the exact function of the PPN is not clear, it is uniquely situated to modulate the influence of the basal ganglia on locomotion and balance. Higher cortical centers are also important in the maintenance of gait and balance. The frontal cortex is implicated in the control, coordination, and planning of automatic and voluntary movements. In addition, the posterior parietal cortex is involved in the perception of body position and posture.

Etiology and Classification

Because gait is dependent on the proper functioning and integration of different aspects of the nervous system, a variety of lesions in the central and/or peripheral nervous systems can produce walking difficulties. In a recent series of 120 patients presenting to an outpatient neurology clinic with gait disorder in which patients with hemiparesis, known Parkinson disease (PD), neuroleptic exposure, and orthopedic deformity were excluded, the distribution of etiologies was as follows: myelopathy (17%), sensory deficits (17%), multiple infarcts (15%), parkinsonism (12%), hydrocephalus (7%), cerebellar dysfunction (7%), psychogenic (3%) and toxic/metabolic causes (3%).

Gait disorders can be classified in a number of ways: etiologically ( Box 38.1 ), anatomically ( Box 38.2 ), and clinically ( Table 38.1 and Fig. 38.1 ). Perhaps the most useful approach to understanding gait disorders is a clinicoanatomic one. According to this method, gait disorders can be divided into roughly three anatomic categories: cortical, subcortical, and peripheral. A variety of well-defined clinical gait syndromes can be described under each anatomic rubric.