Prevalence of gastrointestinal symptoms in diabetes mellitus
Several studies have aimed to evaluate the frequency of gastrointestinal symptoms in patients with non-insulin-dependent and insulin-dependent diabetes, but at present no uniform picture can be drawn from these results. An enormous range in the prevalence of gastrointestinal symptoms has been identified in these studies. This probably relates in part to the methodology applied and the types of populations studied. Although gastrointestinal symptoms were usually assessed by either interview or standard questionnaire, the criteria applied to identify relevant symptoms differed between the studies. Few studies compared symptoms in diabetic patients with adequately matched controls. Moreover potential confounders, such as the duration of disease, glycaemic control and the presence or absence of autonomic neuropathy or psychiatric disorders, were not corrected for in most of the studies.
An ideal study of the epidemiology of gastrointestinal symptoms needs to take into account a number of issues specific to patients with diabetes. An unselected sample of the diabetes population should be compared to an appropriately matched control population. The control group for population-based studies should be selected at random from the healthy population. However, for outpatient studies disease controls are usually more appropriate than healthy controls because the selection forces differ in the clinic. The populations studied need to be carefully characterised, including by age and sex, type and duration of diabetes, type and success of therapy, the presence or absence of diabetic complications, and the type of complications. It is of particular importance that symptoms are assessed by adequately validated measures. However, although validated measures that evaluate gastrointestinal symptoms exist for a variety of diseases, no diabetes mellitus-specific questionnaire has been widely available. Recently, a disease-specific questionnaire, the Diabetes Bowel Symptom Questionnaire (DBSQ), has been developed for use in both epidemiological and clinical studies of patients with diabetes. The items included in this questionnaire assess both gastrointestinal symptoms in diabetes as well as diabetic disease status, and the instrument appears to be reliable and valid.