Asymptomatic common bile duct dilation and methadone use: Re-examining the link in minority inner-city populations

Introduction Opiates have long been implicated in causing common bile duct (CBD) dilation but few studies have been done to look at the association between synthetic opiate -Methadone and asymptomatic CBD dilation. The mechanism by which methadone could cause CBD dilation is poorly understood, but it has been postulated that increase in biliary pressures from Sphincter of Oddi contraction is likely. We conducted a retrospective singlecenter observational study to elucidate the correlation between methadone use and CBD size measured on Ultrasonography (USG). Methods We retrospectively reviewed charts of 444 patients who underwent USG of the abdomen between 2010 and 2015. The patients were divided into two groups. Patients on methadone at the time of USG were included in the study group (n= 171) while those not on methadone were included in the control group (n= 273). Patients with diagnosis of cirrhosis, pancreatitis, choledocholithiasis or other CBD obstruction, patients who had undergone cholecystectomy and were on non-methadone opiates were excluded from the study. Demographic data including age, gender and ethnicity of the patients were reviewed. Laboratory parameters to include liver enzymes (AST, ALT and ALP), bilirubin levels and radiological parameter of CBD size (in mm.) were tabulated. Statistical analysis of the data included t-test analysis for continuous variables, Fisher exact test for categorical variables, Kendall's rank correlation test and multivariate logistic regression analysis. Results The mean age of the study group (53.09 ± 9.50 years) was significantly higher than that of the control group (48.08 ± 9.50 years) (p-value =0.0013). The distribution of gender (p-value =0.24) and ethnicity (p-value =0.22) was similar among the two groups. The CBD size was significantly greater in the study group (5.70 ± 3.26 mm) when compared to control group (3.98 ± 1.11mm) after adjusting for age, gender and ethnicity (p-value = 3.839e-10). There was also a signficant correlation between the CBD size and dose of methadone after adjusting for age, which was not seen in prior studies. There was no correlation between CBD size and either- ALP (p-value = 0.09) or serum total bilirubin (pvalue = 0.12). Conclusion To our knowledge, this study is the largest of its kind to date, in terms of the size of the study population and predominantly includes inner-city minority populations. Patients on methadone were found to have significantly higher prevalence of dilated CBD when compared to patients, not on methadone. Dose of methadone was also found to have a positive correlation with CBD size. However, the degree of CBD dilation seemed to have no implications on liver enzyme or bilirubin levels.