Parkinson disease.

Parkinson disease (PD) is a complex, multisystem disorder with both neurologic and systemic nonmotor manifestations. It is neurodegenerative in nature in which disordered balance, gait, and falls are universal problems that can be present at initial diagnosis, and which progress over time. Freezing of gait is a particularly debilitating feature of PD that becomes more prevalent over time with disease progression, being present in approximately 7% after 2 years of disease and 28% after 5 years. Approximately 60% of people with PD fall each year, with around 70% of fallers falling recurrently, and some recurrent fallers falling multiple times per week. Many risk factors for falls in people with PD have been identified; these include a history of falls, freezing of gait, and abnormalities in measures of balance, leg muscle strength, mobility, cognition, and fear of falling. Therapies for improving physical function and mobility include levodopa, cholinesterase inhibitors, methylphenidate, deep-brain stimulation, cuing for freezing of gait, and exercise. This chapter reviews the clinical, pathologic, and physiologic correlates of gait disturbance and falls in PD, as well as the evidence for medical and nonmedical interventions.