The Non-Motor Prodromal Symptoms of Parkinson's Disease: A Review

Parkinson's disease is a common progressive neurodegenerative disorder with both motor and non-motor symptoms. There is no clear etiology, and it has no cure. The non-motor features often precede the motor symptoms by many years, so they are considered prodromal symptoms of the disease. These symptoms include olfactory dysfunction, constipation, sleep problems, and depression. The purpose of this study is to review the literature on Parkinson's disease non-motor prodromal symptoms and their role from the early stages throughout the disease's development. The review discusses several aspects related to the prodromal features of Parkinson's disease: their prevalence in Parkinson's disease patients, the pathophysiology, the treatment, if it is possible, and the prodromal symptoms' effect on the diagnosis, prognosis, and management of the disease, in addition to their impact on patients' quality of life. More studies are required to precisely pinpoint the timing of non-motor prodromal symptoms onset and modify the diagnostic criteria for Parkinson's disease accordingly. KEYWORDS constipation, depression, gastrointestinal dysfunctions, hyposmia, olfactory dysfunction, sleep disturbances