Autonomic nervous system and gastrointestinal manifestations with an emphasis on gastric dysfunction

Gastrointestinal (GI) symptoms are frequent in disorders that involve the autonomic nervous system (ANS) or the enteric neuromuscular apparatus. Although dysfunction may occur anywhere along the alimentary tract, gastric manifestations are often the most clinically visible 'end-organ' expression of autonomic disease because they drive nausea, vomiting, early satiety, postprandial distress, malnutrition risk, and impaired drug absorption. In this invited review, we summarize the organization of the GI neuromuscular apparatus, emphasizing how intrinsic (enteric) circuitry and extrinsic sympathetic and parasympathetic pathways cooperate to regulate gastrointestinal functions. We then link common symptom clusters (dysphagia, gastroparesis, intestinal pseudo-obstruction, constipation, diarrhea, and fecal incontinence) to likely neuroanatomic levels and review autonomic test batteries and motility studies that help characterize dysfunction. Finally, we discuss neurologic and systemic diseases in which autonomic and enteric involvement produce prominent gastric and broader GI phenotypes. These include cerebrovascular and cortical neurodegenerative disorders, Parkinson's disease, structural and inflammatory brainstem syndromes, primary autonomic failure and hereditary dysautonomia, postural orthostatic tachycardia syndrome, spinal cord disorders (including multiple sclerosis), peripheral neuropathies such as diabetes mellitus and amyloidosis, paraneoplastic and autoimmune autonomic neuropathies, and selected neuromuscular and myopathic conditions.