The epidemiology of primary biliary cirrhosis.

Over the last 30 years, many studies have reported on the epidemiology of PBC. Substantial increases in prevalence were noted in the majority of studies examining longitudinal data, and several have reported increases in the incidence of PBC. Furthermore, although it is difficult to compare studies directly, as methods of case ascertainment have greatly improved over this period, there has been a definite trend toward increasing prevalence (and also possibly incidence) across studies. Together, these data strongly suggest that in many countries, the frequency with which PBC is diagnosed has increased considerably between 1980 and the present time. The reasons for this change may be complex. There may have been a true increase in the incidence of PBC, reflecting either increased exposure to a currently unknown environmental etiological agent or demographic changes with an increased elderly, at-risk population. The prevalence may have further increased due to increased survival of patients, either due to improved care or earlier diagnosis. Some of the apparent increase in PBC frequency may also be artifactual, however, resulting from increased use of diagnostic tests, particularly autoantibody screens. This may be due to increased availability of testing, increased clinician (or patient) awareness of PBC, increased use of testing in well-person screening, or increased investigation of ill-defined symptoms. Furthermore, there may also have been an improvement in clinicians' ability to recognize PBC on the basis of the clinical picture (in one study, 37% of patients whose clinical results indicated a diagnosis of PBC were not recognized by the clinician caring for the patient at that time). The last factor alone suggests that all studies based only upon cases known to interested clinicians have probably substantially underestimated the prevalence of disease. Whatever the reason, the recognized epidemiology of PBC has dramatically changed over the past 30 years. It is now a frequent cause of liver morbidity, and patients with PBC are significant users of health resources, including liver transplantation. Large geographical variations in disease frequency, both between and within studies, tantalizingly suggest the presence of as-yet-unidentified risk factors. This should be further followed up with new analytical epidemiological studies. Only two case control studies have examined risk factors for PBC, and these have been either relatively small or used poorly defined and potentially biased experimental groups. These need repeating in new settings. We suggest that, as with other diseases, modern epidemiological instruments used in well-designed studies may provide important clues to the cause or causes of this disease.