Melatonin and dopamine serum level associations with the motor, cognitive, and sleep dysfunctions in patients with Parkinson's disease: A cross-sectional research study.

BACKGROUND: Parkinson's disease (PD) is a multisystem-progressive neurodegenerative disease characterized by dopaminergic neurons, however, the role of the non-dopaminergic system (such as melatonin hormone) in the pathogenesis of PD is now emerging.

OBJECTIVE: To identify any potential correlation between the dopamine and melatonin serum levels, and motor, cognitive, and sleep dysfunctions in patients with PD.

METHOD: Cross-sectional piloting study conducted with a sample of 34 patients with PD (aged 50-72 yrs. old). Correlation tests performed to identify any potential correlations between the biomarkers' serum levels and motor, cognitive, and sleep dysfunctional levels in "on-medication" status.

RESULTS: Spearman's test showed significant correlations between the melatonin serum level and sleep dysfunctions including; overall sleep quality (P = 0.010) and subjective sleep quality sub-score (P = 0.001). On the other hand, spearman's test showed significant correlations between the dopamine serum level and motor dysfunctions including; Berg Balance Scale (P = 0.026), 10-Meters Walking Test (P = 0.016), and Fearing of Fall index (P = 0.007), as well between the dopamine serum level and cognitive dysfunction (P = 0.048).

CONCLUSIONS: Melatonin serum level would serve as a potential biomarker in understanding the PD pathogenesis, and consider the melatonin serum level in the future study related to PD besides to the dopamine serum level.