Prevalence of Mixed Connective Tissue Disease in a Population-Based Registry of American Indian/Alaska Native People in 2007

Objective. To determine the prevalence of mixed connective tissue disease (MCTD) in 2007 in the Indian Health Service (IHS) active clinical population from 3 regions of the US. Methods. The IHS Lupus Registry was designed to identify possible MCTD cases in addition to systemic lupus erythematosus cases. The population denominator for this report includes American Indian or Alaska Native adults within the IHS active clinical population in 2007, residing in select communities in 3 regions of the US. Potential MCTD cases were identified using a broad range of diagnostic codes and were confirmed by detailed medical record abstraction. Classification as MCTD for this analysis required both rheumatologist diagnosis of MCTD without diagnosis of other CTD, and documentation of the Alarcon-Segovia MCTD criteria in the medical record. Prevalence was also calculated using 2 alternate definitions of MCTD. Results. The age-adjusted prevalence of MCTD using our primary definition was 6.4 per 100,000 (95% confidence interval 2.8-12.8). The prevalence was higher in women than in men using all 3 definitions of MCTD, and no men met the criteria for the primary definition of MCTD. Conclusion. The first population-based estimates of the prevalence of MCTD in the US American Indian/Alaska Native population show that the prevalence appears to be higher than in other populations. Additional population-based estimates are needed to better understand the epidemiology of MCTD.