Functional lower gastrointestinal disorders include irritable bowel syndrome (IBS), functional constipation, functional fecal incontinence, and functional anorectal pain. These disorders are common and have significant medical and social effects. They also can be challenging to manage. Patients with mild symptoms may benefit from lifestyle modification. IBS is classified into two subtypes: diarrhea-predominant and constipation-predominant. Depending on the IBS subtype and its likely etiology, patients may benefit from treatment with antispasmodics, antidepressants, guanylate cyclase-C agonists, chloride channel activators, antidiarrheal agents, probiotics, and/or antibiotics. Functional constipation responds to many of the same treatments as constipation-predominant IBS, which include guanylate cyclase-C agonists and chloride channel activators. The management of functional fecal incontinence includes behavioral therapy, relief of constipation (disimpaction, bulking agents), and antidiarrheal drugs. Functional anorectal pain management has not been well studied, but patient symptoms may improve with physical therapy, antispasmodics, nerve block, or onabotulinumtoxinA injection.
