Literature Review: Parkinson's Disease and Non-Motor Symptoms, with a Focus on Constipation and Potential Therapeutics

Parkinson’s Disease (PD) is a progressive neurodegenerative disorder that tends to affect elderly individuals and is most commonly associated with the emergence of motor symptoms such as tremors, stiffness, and bradykinesia. However, non-motor symptoms (NMS), such as gastrointestinal (GI) issues, namely constipation, are also prevalent, and deeply affect the lives of individuals suffering with the disease. Among these, constipation stands out as one of the most common and frustrating problems for patients, typically arising from a variety of interrelated factors including disruptions in the autonomic nervous system (ANS), diminished dopamine activity, gut microbiota imbalances, inflammation, and side effects from PD medications. Constipation can worsen other PD symptoms by slowing medication absorption (significantly reducing its’ effectiveness), whilst also increasing fatigue and depression, thus highlighting the need for a comprehensive approach to PD treatment that includes addressing this issue. Promising options for managing constipation are offered by emerging therapies such as vagus nerve stimulation (VNS) and focused ultrasound stimulation (FUS), but further research is still needed to fully understand the mechanisms and to confirm their safety and efficacy. This review highlights the importance of early detection and management of constipation in PD to improve symptoms, better manage the disease, and ultimately enhance the quality of life for patient