Impact of diabetes mellitus type two on incidence and progression of Parkinson's disease: a systematic review of longitudinal patient cohorts.

Parkinson's disease (PD) is a chronic neurodegenerative disease of the elderly. Patients suffer from progressive motor and non-motor symptoms. Further, PD patients often present geriatric features like multimorbidity and polypharmacotherapy. A frequent comorbidity of PD patients is diabetes mellitus type two (T2DM). In the last decade growing evidence emerged on the impact of T2DM on PD. Of the present review was to analyze the impact of T2DM on PD incidence and progression in patient cohorts. A systematic review of the literature was performed via PubMed and Google Scholar. Studies on longitudinal PD patient cohorts with at least 10 patients per group were included. The diabetic state of the patient had to be determined. In total, 15 studies were analyzed for this review. According to most of the included studies T2DM increases the risk of developing PD significantly. Disease progression is augmented by T2DM both for motor and cognitive impairments. Some studies also point out a correlation of motor worsening and diabetic status measured by the serum HbA1c level. In relation to biomarkers, PD patients with diabetes have higher neurofilament light chain and Tau level but lower Amyloid beta level. T2DM seems to be a risk factor for the development and progression of PD. PD patients should be screened for T2DM and treatment should be initiated promptly. There is still a lack of knowledge about the molecular mechanisms leading to interactions of these diseases.