Axial disability and deep brain stimulation in patients with Parkinson disease.

Axial motor signs-including gait impairment, postural instability and postural abnormalities-are common and debilitating symptoms in patients with advanced Parkinson disease. Dopamine replacement therapy and physiotherapy provide, at best, partial relief from axial motor symptoms. In carefully selected candidates, deep brain stimulation (DBS) of the subthalamic nucleus or globus pallidus internus is an established treatment for 'appendicular' motor signs (limb tremor, bradykinesia and rigidity). However, the effects of DBS on axial signs are much less clear, presumably because motor control of axial and appendicular functions is mediated by different anatomical-functional pathways. Here, we discuss the successes and failures of DBS in managing axial motor signs. We systematically address a series of common clinical questions associated with the preoperative phase, during which patients presenting with prominent axial signs are considered for DBS implantation surgery, and the postoperative phase, in particular, the management of axial motor signs that newly develop as postoperative complications, either acutely or with a delay. We also address the possible merits of new targets-including the pedunculopontine nucleus area, zona incerta and substantia nigra pars reticulata-to specifically alleviate axial symptoms. Supported by a rapidly growing body of evidence, this practically oriented Review aims to support decision-making in the management of axial symptoms.