Autonomic abnormalities in children with functional abdominal pain: Coincidence or etiology?

Background: There is increasing evidence that autonomic neuropathies may adversely affect gastrointestinal motility by involving the extrinsic nerves of the gut. The authors' hypothesize that functional abdominal pain in children is associated with generalized autonomic dysfunction. Methods: The authors performed detailed autonomic testing in eight patients with functional abdominal pain, including deep breathing, Valsalva, tilting (to assess parasympathetic and sympathetic adrenergic function), and axon-reflex function and thermoregulatory sweat testing to assess sympathetic cholinergic function. Patients also completed a questionnaire regarding other autonomic symptoms. Results: Results of autonomic testing were abnormal in seven patients. Parasympathetic function was normal in all, and the abnormalities were restricted to sympathetic cardiac, vasomotor, and sudomotor function. Abnormal results of axon-reflex testing in six were consistent with peripheral nervous system dysfunction. Five had decreased sweating over the abdomen, determined by thermoregulatory sweat testing. Five eight had nongastrointestinal autonomic symptoms, primarily palpitations and flushing. Conclusions: Functional abdominal pain in the current patients is associated with generalized dysfunction of the autonomic nervous system. This dysfunction can be peripheral or central in different individuals but seems to be restricted to the sympathetic branch. The known function of the sympathetic nervous system as the motility "brake" suggests that pain could be a manifestation of unmodulated peristalsis, resulting in abdominal cramps.