Cough reflex sensitivity in adolescents with diabetic autonomic neuropathy

OBJECTIVE Diabetic autonomic neuropathy (DAN) is one of the chronic complications of diabetes mellitus which can involve one or more organ systems. DAN without apparent symptoms is more often in childhood and adolescence. While heart rate variability (HRV) and Ewing's battery of cardiovascular tests are regarded as a gold standard for the diagnosis of DAN, the examination of cough reflex sensitivity (CRS) is another possibility. The aim of this study was to compare HRV and CRS in children with diabetes mellitus. MATERIAL AND METHODS Sixty one patients (37 girls, 24 boys) aged 15-19 suffering from diabetes mellitus type 1 completed the study. Based on HRV, patients were divided into 2 groups - with DAN (n=25) and without DAN (n=32), 4 patients were excluded because of ambiguous results. CRS was studied in each patient by inhalation of gradually increasing concentration of capsaicin. RESULTS Subjects with DAN required a significantly higher concentration of capsaicin needed to evoke 2 coughs (median 625 micromol/l, IQR 68.4-625.0 micromol/l vs. median 29.3 micromol/l, IQR 9.8-156.3 micromol/l, P<0.001) and 5 coughs (median 2500.0 micromol/l, IQR 1250.0-2500.0 micromol/l vs. median 312.5 micromol/l, IQR 117.2-625.0 micromol/l, P<0.001) compared with those without DAN. Moreover, a strong negative correlation between HRV and CRS was established. CONCLUSION Diabetes mellitus lowers the cough response. Cough reflex sensitivity appears to be another sensitive method for the evaluation of DAN in diabetes.