Diabetic neuropathy in the gut: pathogenesis and diagnosis

The activity of the digestive tract is usually regulated to match its content: physiological stimuli in the gut induce modulatory reflexes that control digestive function so that digestion is normally not perceived. However, under certain circumstances, digestive stimuli may activate sensory afferents and give rise to conscious sensations. Both reflex and sensory signals are modulated by a balance of excitatory and inhibitory mechanisms. Patients with diabetes may develop a neuropathy affecting the control of gastric and/or intestinal motor function and the sensory innervation as well. During fasting the stomach is contracted and relaxes to accommodate a meal. After ingestion the stomach progressively recontracts and this contraction gently produces gastric emptying. Impairment of excitatory pathways affects the contraction of the stomach, which may result in delayed gastric emptying and vomiting of retained food. Conversely, alteration of the inhibitory neural pathways results in impaired relaxation of the stomach in response to a meal; in this case increased wall tension may produce early satiation, fullness and nausea. Diabetic neuropathy may distort the control of intestinal motility, which can lead to diverse symptoms such as diarrhoea, constipation, intestinal distension and abdominal pain. Neuropathy in diabetes may also affect the sensory nerves of the gut, and depending on which pathways are involved, perception may be increased or reduced. In summary, in patients with diabetic neuropathy, disorders of gut motor function are associated with sensory abnormalities, and the combination of impaired pathways determines the clinical consequences. This review summarises a presentation given at the 'Diagnosis and treatment of autonomic diabetic neuropathy in the gut' symposium at the 2015 annual meeting of the EASD. It is accompanied by another mini-review on a topic from this symposium (by Hans Tornblom, DOI: 10.1007/s00125-015-3829-9) and a commentary by the Session Chair, Peter Kempler (DOI: 10.1007/s00125-015-3826-y).