Parkinson disease (PD) is a clinical entity characterized by bradykinesia, rigidity, tremor, and postural instability. Current treatments primarily focus on replacement of dopamine to compensate for the degeneration of the substantia nigra pars compacta dopaminergic neuronal population. Though dopamine treats many of the motor symptoms of PD, postural instability (which often leads to falls) typically is least responsive to therapy. More recently, the degeneration of the cholinergic system arising from the pedunculopontine nucleus (PPN) in the brainstem has been implicated in gait dysfunction in PD. Striatal cholinergic inputs are supplied from the PPN both via the intralaminar complex of the thalamus and through direct inputs. The primary subtypes of cholinergic receptors present in the striatum are nicotinic and include α4β2, α6β2, and α7 receptors. Varenicline (Chantix) is a novel partial α4β2 agonist and full α7 agonist developed as an aid for smoking cessation and has been shown in initial studies to improve imbalance in patients with inherited spinocerebellar ataxia. The unique method of action of varenicline may make it an ideal drug for the treatment of balance impairment in PD.
The purpose of this study is to determine if varenicline is effective in improving gait and balance impairment in patients with Parkinson disease.