The relationship between inflammatory bowel disease and Parkinson's disease: true or fiction?

Gastrointestinal (GI) symptoms can precede by many years the motor symptoms of Parkinson's disease (PD) and these patients can show some degree of inflammation associated with abnormal aggregates of alpha-synuclein in the GI tract. The abnormal accumulation of alpha-synuclein and the spreading of the aggregates from the gut to the brain might be promoted by inflammation, rising the hypothesis of a possible relationship between inflammatory bowel disease and PD. Many population-based studies have explored this association, but they have found conflicting results. It is essential to clarify this hypothesis and to try to elucidate the milestones of this relationship. There is no clear concordance between the results and the interpretation of different previous findings, probably due to many confounding factors such as drugs with anti-inflammatory activity, surgery, genetic predisposition and also selection bias. If there is a real association between both diseases, gastroenterologists and neurologists should be able to detect possible triggers of the disease or on the other hand, protective factors, that may be considered in clinical practice.