Deep brain stimulation in Parkinson's disease: Looking back, looking forward

Patients with Parkinson’s disease (PD) may present with prodromal (e.g. hyposmia, sleep disorders, constipation), motor (e.g. tremors, rigidity, bradykinesia, postural dysfunction) and non-motor (e.g. cognitive dysfunction, depression) symptoms.1 Treatment is symptomatic, targeting motor and non-motor manifestations, but there is presently no effective disease modifying treatment.1 Although PD therapies have primarily been focused on supplementing dopamine, which has improved survival and quality of life of PD patients,1-3 other neurotransmitter systems (e.g. serotonergic, cholinergic and noradrenergic) are also dysfunctional, especially for the non-motor symptoms.1,4,5 By the time patients reach the later stages of PD, many of them would have developed significant gait and balance difficulties, dysarthria, dysphagia and motor fluctuations like wearing off and levodopa-induced dyskinesias (LID), as well as non-motor symptoms such as orthostasis, depression, dementia and psychosis.1,2,6,7