The PanGut-study: Evoked potentials following rectal balloon distention, a way of evaluating diabetic autonomic neuropathy in the gut?

Diabetic gastroenteropathy: a pan-alimentary complication

Autonomic neuropathy contributes to the pathophysiology of diabetic gastroenteropathy, which impacts the entire gastrointestinal tract alongside pancreatic and gallbladder functions. This is evident in the widespread morphological remodelling of the enteric nervous system, smooth muscle cells, interstitial cells of Cajal and vascular supply, causing pan-enteric motor, sensory and secretory disturbances. The gastrointestinal symptoms caused by these changes are often burdensome and non-specific and frequently coexist with poor glycaemic management and even malnutrition, impacting quality of life negatively. The Gastroparesis Cardinal Symptom Index and the Gastrointestinal Symptom Rating Scale are validated questionnaires for assessing gastrointestinal symptoms. However, clinical supplementary objective measures are essential. Transit time assessments are frequently used and typically evaluated using gastric emptying scintigraphy, breath tests or colonic radiopaque markers, but they cannot measure contractile activity or fluid transport. The primary treatment goals are to prevent further disease progression and to obtain symptomatic relief. Treatments include improved glycaemic management and dietary modifications, while pharmacological treatments target gastrointestinal symptoms, small intestinal bacterial overgrowth and exocrine pancreatic insufficiency. Invasive interventions may involve gastric peroral pyloromyotomy or the implantation of a gastric neurostimulator to manage pharmacologically refractory gastroparesis. This review describes the prevalence, pathophysiology, clinical presentation, assessment and treatment of diabetic gastrointestinal dysfunction within each segment of the gastrointestinal tract and directly connected exocrine organs.

Gut Neuropathies and Intestinal Motility Disorders

BACKGROUND

The enteric nervous system plays a key role in the coordination of gastrointestinal motility together with sympathetic, parasympathetic, and extrinsic sensory pathways. In some cases, abnormalities in neural activity in these pathways contribute to disorders of gut motility. Where this is associated with damage or death of enteric neurons, usually detected by microscopy, this is considered a gut neuropathy.

PURPOSE

This review summarizes recent advances in the identification of neuropathies in a range of gastrointestinal motility disorders.

Rectal sensitivity correlated with gastrointestinal-mediated glucose disposal, but not the incretin effect

OBJECTIVE

The mechanisms behind the diminished incretin effect in type 2 diabetes are uncertain, but impaired vagal transmission has been suggested. We aimed to investigate the association between the incretin effect and autonomic neuropathy, and the degree of dysglycaemia and duration of diabetes.

DESIGN AND METHODS

For a cross-sectional study, we included participants with either longstanding type 2 diabetes, recent onset, untreated diabetes and controls without diabetes matched for age, sex and body mass index. Autonomic nerve function was assessed with cardiovascular reflex tests, heart rate variability and sudomotor function. Visceral afferent nerves in the gut were tested performing rapid rectal balloon distention. An oral glucose tolerance test and an intravenous isoglycaemic glucose infusion were performed to calculate the incretin effect and gastrointestinal-mediated glucose disposal (GIGD).

RESULTS

Sixty-five participants were recruited. Participants with diabetes had rectal hyposensitivity for earliest sensation (3.7 ± 1.1 kPa in longstanding, 4.0 ± 1.3 in early), compared to controls (3.0 ± 0.9 kPa), p = .005. Rectal hyposensitivity for earliest sensation was not associated with the incretin effect (rho = -0.204, p = .106), but an association was found with GIGD (rho -0.341, p = .005). Incretin effect and GIGD were correlated with all glucose values, HbA1c and duration of diabetes.

CONCLUSIONS

Rectal hyposensitivity was uncovered in both longstanding and early type 2 diabetes, and was not associated with the incretin effect, but with GIGD, implying a potential link between visceral neuropathy and gastrointestinal handling of glucose. Both the incretin effect and GIGD were associated with the degree of dysglycaemia and the duration of diabetes.

PREVIOUSLY PUBLISHED

Some of the data have previously been published and presented as a poster on the American Diabetes Association 83rd Scientific Sessions: Meling et al; 1658-P: Rectal Hyposensitivity, a Potential Marker of Enteric Autonomic Nerve Dysfunction, Is Significantly Associated with Gastrointestinally Mediated Glucose Disposal in Persons with Type 2 Diabetes. Diabetes 20 June 2023; 72 (Supplement_1): 1658-P. https://doi.org/10.2337/db23-1658-P.

The Composite Autonomic Symptom Score 31 Questionnaire: A Sensitive Test to Detect Risk for Autonomic Neuropathy

Background and Aims

Autonomic neuropathy is a common but often neglected complication of diabetes, prediabetes, and even in individuals with an elevated risk of diabetes. The Composite Autonomic Symptom Score (COMPASS) 31 is a validated and easy-to-use questionnaire regarding autonomic symptoms. We aimed to use a digitally, Norwegian version of the COMPASS 31 in people with different durations of diabetes and healthy controls to consider feasibility and to investigate if scores could discriminate between positive and negative outcomes for established tests for diabetic neuropathy, including cardiovascular autonomic neuropathy (CAN) and a novel method of examining the gastrointestinal visceral sensitivity.

Method

We included 21 participants with longstanding type 2 diabetes, 15 with early type 2 diabetes, and 30 matched controls. The mean age for all groups was 69 years. Participants were phenotyped by cardiovascular autonomic reflex tests, electrical skin conductance, sural nerve electrophysiology, and the monofilament test. As a proxy for gastrointestinal visceral and autonomic nerve function, evoked potentials were measured following rapid rectal balloon distention.

Results

Participants with longstanding diabetes scored a median (IQR) of 14.9 (10.8-28.7) points, early diabetes of 7.3 (1.6-15.2), and matched controls of 8.6 (4.1-21.6), p = 0.04. Women and men scored 14.4 (5.5-28.7) and 7.8 (3.6-14.6) points, respectively, p = 0.01. Participants with definite or borderline CAN scored 14.3 (10.4-31.9) points, compared to participants with no CAN, 8.3 (3.2-21.5), p = 0.04. Lowering the diagnostic cut-off from 16 to 10 points increased the sensitivity from 0.33 to 0.83, with a decreased specificity from 0.68 to 0.55.

Conclusion

We successfully used COMPASS 31 in Norwegian. Thus, following the guidelines, we suggest clinical implementation for the assessment of autonomic neuropathy. Participants with longstanding diabetes had an increased likelihood of symptoms and signs of autonomic neuropathy. For screening purposes, the sensitivity was improved by lowering the cut-off to 10 points, with a lower score nearly excluding the diagnosis.