Movement disorders associated with diarrhoea

Although the bidirectional relationship between the central nervous system and the gut has gained increasing attention in neurodegenerative conditions and movement disorders, much of the focus seems to be on constipation and other symptoms related to gastrointestinal hypomotility. However, intestinal hypermotility-related symptoms, such as diarrhoea, are also frequently associated with movement disorders, representing a clinical and research gap that needs to be addressed. This narrative review aims to describe the movement disorders associated with diarrhoea as a gastrointestinal manifestation and provide a useful overview for routine clinical practice. A variety of acquired causes, such as infectious, toxic, metabolic, and autoimmune, as well as inherited conditions may present with diarrhoea; in fact, loosen stool may sometimes precede the onset of movement disorders. Furthermore, the characteristics and volume of diarrhoea may vary depending on the underlying condition, as different pathophysiological mechanisms affecting the central and peripheral nervous system may alter gastrointestinal function. Diarrhoea is a prominent clinical symptom across a wide range of conditions, particularly those manifesting with hyperkinetic movement disorders, such as ataxia, myoclonus and tremor. When occurring in conditions with predominant hypokinetic movement disorders, it is mostly drug-associated or presents as overflow diarrhoea. Further studies exploring the relationship between bowel hypermotility and neurological dysfunction are needed.