Parkinson’s disease, progression tends to be slow and variable. Doctors often use the Hoehn and Yahr scale to gauge the progression of the disease over the years. The scale was originally implemented in 1967 and it included stages zero to five, where zero is no signs of Parkinson’s and five is advanced PD. It was later changed to become the modified Hoehn and Yahr scale. In addition to movement-related (“motor”) symptoms, Parkinson’s symptoms may be unrelated to movement (“non-motor”).People with PD are often more impacted by their non-motor symptoms than motor symptoms. Examples of non-motor symptoms include: apathy, depression, constipation, sleep behavior disorders, loss of sense of smell and cognitive impairment.because a significant amount of the substantia nigra neurons have already been lost or impaired. Lewy bodies (accumulation of abnormal alpha-synuclein) are found in substantia nigra neurons of PD patients. Scientists are exploring ways to identify biomarkers for PD that can lead to earlier diagnosis and more tailored treatments to slow down the disease process. Currently, all therapies used for PD improve symptoms without slowing or halting the disease progression.