Gastrointestinal system

Rheumatic diseases and diseases of the gastrointestinal (GI) tract are connected in two ways. The extraintestinal manifestations of inflammatory GI diseases such as inflammatory bowel disease affect joints in up to one-third of patients. On the other hand, several rheumatic diseases such as vasculitis or systemic lupus erythematosus (SLE) induce a wide spectrum of gastrointestinal manifestations. The GI tract constitutes a huge area in contact with the environment. It is exposed to billions of food antigens, commensal bacteria, and potential pathogens. Some of those antigens are thought to play a role in the pathogenesis of rheumatic diseases. The intestinal barrier function and the gut immune system are tightly regulated, as on one hand tolerance for food antigens and the resident commensal flora needs to be maintained, and on the other hand pathogens need to be rapidly and effectively eliminated. Non-infectious, chronic inflammatory diseases of the small and large intestine with rheumatic manifestations have been well known for decades. Among the susceptibility genes for Crohn's disease and ulcerative colitis are some that also cause susceptibility to rheumatoid arthritis or SLE, indicating a shared susceptibility and overlapping pathological mechanisms. Subsequently, similar therapeutic principles have successfully been applied in autoimmune GI and rheumatological diseases such as steroids, immunosuppressants, and anti-TNF (tumour necrosis factor) antibodies.