Using the State Inpatient Databank, we identified a significant regional variability in hospitalizations and operations for biliary dyskinesia. While the differences in demographic characteristics, such as rates of poverty or obesity, potentially contribute to these differences, they are not the main factors as shown by our analysis. Independent of the results of statistical testing, a six-fold difference in hospitalizations for biliary dyskinesia between Maine and West Virginia is difficult to reconcile with presumed differences in disease mechanisms, as both states have a relatively low population density with the majority living in smaller, mostly rural communities, with Caucasians making up more than 90% of the population and without strikingly different adult obesity or poverty rates. Consistent with the results of our statistical assessment, the differences between these two states also extends to admissions for gallstone disease and overall hospitalization rates, pointing more at established practice patterns than biological causes as the underlying cause. The importance of established patterns is further supported by the close correlation between cholecystectomies for complications of gallstone disease and the rate of surgical treatment for biliary dyskinesia, and may well go beyond the approach to biliary disease. Beyond factors examined in this study, regional differences in the organization of healthcare delivery or the health insurance market may contribute to this pitcture. Lastly, similarities between neighboring states described above may be a reflection of similarities in medical training, which does not only affect medical decision making, forming a culture of medical reasoning and decision-making, but also practice locations, as the majority of physicians choose practices in relatively close proximity to the location of their residency.5,6
Established or changing practice patterns have previously been shown to influence the approach to biliary diseases. The introduction of laparoscopic techniques resulted in a significant increase in cholecystectomies with a shift to more elective operations in younger, low risk patients with chronic symptoms.7-9
Independent of such innovations, others have reported regional differences in the management of gallbladder disease that cannot be explained by variability of demographic characteristics or availability of medical services. For example, treatment of acute cholecystitis varied significantly within a region or even a single city.10,11
Consistent with a role of practice location and practice patterns, a prior study demonstrated that biliary dyskinesia is more commonly diagnosed by surgeons in rural settings.12
We did not identify a correlation between cholecystectomy rates and patients with rural residence or treatment in a rural hospital. However, a low population density and fewer practicing physicians within a state, both variables associated with rural environments, were independent predictors for admission and/or surgery rates for biliary dyskinesia.
While lower than in biliary dyskinesia, we also noted regional variability in the approach to cholelithiais/cholecystitis. As was the case for biliary dyskinesia, regional differences in practice patterns contributed to this variability, as overall annual hospitalizations independently predicted the rate of admissions for complications of gallstone disease, when controlling for obesity, poverty, age and racial composition of the different states. Our findings fit into a larger picture, demonstrating regional variations in healthcare utilization, which influences the choice of diagnostic testing, medical or surgical therapy10-17
and may be confounded by physician or patient preference, difference in insurance status and demographic or economic factors.12,15,18
The study has several important limitations. First, biliary dyskinesia does not have a distinct diagnosis code. Using a validation sample with a detailed analysis of medical records, we have previously shown that biliary dyskinesia accounted for more than 80% of the patients with the ICD-9 code 575.8 as the primary diagnosis code. The validation study was based on a single medical center. Thus, regional variability in coding could affect our results, but is unlikely to explain the seven-fold difference in admission rates. As is true for all studies based on large databanks, correlations do not proof causality. The analyses combined data from different sources, not allowing us to truly relate obesity as a potentially relevant comorbid condition to biliary disease. We used the published rates for adult obesity within states and may thus underestimate its true impact on the manifestations of biliary disease. In addition, some variables may simply be indicators or surrogate markers of other influences that were not included. For example, poverty levels are often also associated with lower educational achievements and different dietary habits. Finally, all data are based on admissions, not patients. Therefore, repeat admissions could skew the results. Considering cholecystectomy rates of about 70%, the contribution of such repeated admissions will not account for a large number of hospitalizations.
Despite these limitations, the results fit into a bigger picture. The significant variability in admissions for biliary dyskinesia as central finding is consistent with prior studies suggesting a significant impact of socioeconomic rather than biological factors in the diagnosis of biliary dyskinesia as an indication for cholecystectomy.3,12
European experts question the utility of functional gallbladder testing in diagnosing a clinically relevant disorder or predicting treatment outcomes.4
While it has never been systematically analyzed, the approach to presumed functional disorders of the biliary tree seems to differ even more strikingly on a global level. Published case series of pediatric patients undergoing cholecystectomies did not include biliary dyskinesia in European studies,19-22
while it accounts for up to more than 50% of the operations in the United States.23-28
Focusing on adult patients, a meta-analysis of surgical case series describing the outcomes after cholecystectomy for biliary dyskinesia similarly only identified studies conducted in the United States.29
In contrast, meta-analyses focusing on surgical techniques or antibiotic prophylaxis for cholecystectomy identified studies performed in multiple countries including the United States.30-33
In conclusion, admissions and operations for biliary dyskinesia are at least partly driven by practice patterns, with regional variations likely reflecting differences in threshold for operative interventions. No study has ever addressed the natural history of biliary dyskinesia. While cholecystectomy may be associated with symptomatic improvement, long-term results suggest a lessening benefit and show an ongoing impairment of quality of life measures,34
findings that fit into our understanding of the natural history of other functional gastrointestinal disorders.35,36
Considering the benign natural history of gallstone disease37
and the risk of cholecystectomy, it is time to study the natural history of this syndrome and test non-operative interventions that have shown benefit in related disorders, such as functional dyspepsia.