Beyond the brain: The colorectal impact of Parkinson's disease

Parkinson's disease (PD) is a rapidly developing neurodegenerative disorder characterized by degeneration of dopaminergic neurons in the basal ganglia of the brain. Its prevalence is estimated to exceed 1.2 million cases in the United States by 2030. Emerging evidence suggests that PD may originate in the gut and hence is linked to gastrointestinal (GI) dysfunctions such as inflammatory bowel disease and GI cancers. Colorectal cancer (CRC) is one of the most common cancers seen worldwide. It shares several risk factors with PD, including advancing age, male gender, genetic predispositions, and environmental exposures. Although these shared factors indicate a possible correlation, the studies evaluating this relationship have suggested inconsistent results. Some research proposes an increased risk of CRC in PD patients, potentially due to overlapping genetic and inflammatory pathways. Alternatively, others argue an inverse relationship due to opposing underlying mechanisms of neuro degeneration in PD and cellular proliferation in CRC. This narrative review explores the intricate relationship between PD and CRC and seeks to understand how neurodegenerative and malignant diseases may overlap.