Background/Purpose

Patients with polymyositis (PM) and dermatomyositis (DM) may have an increased risk of myocardial infarction (MI), similar to other connective tissue diseases. However, no relevant data are scarce to date. We estimated the future risk and time trends of newly recorded cases of MI among individuals with incident PM/DM (1996-2010) compared to controls using physician-billing data from the province of British Columbia (~4.4 million).

Methods

Our data include all visits to health professionals and all hospital admissions, investigations (1990-2010) and all dispensed medications (1995-2010) for all individuals. We conducted a retrospective matched cohort study. Ten controls matched by birth year, sex and calendar year were randomly selected from the general population for each case. Outcome: Newly recorded MI events during follow up from hospitalization (ICD-9CM 410 or ICD-10 code: I21). In addition, we defined death from MI based on the death certificate diagnostic codes, including out of hospital deaths (ICD-10 code: I21). We calculated incidence rate ratios (IRR) overall and stratified by disease duration. We calculated hazard ratios (HR) and 95% confidence intervals (95% CI) adjusting for relevant confounders. Sensitivity analyses were conducted to assess for unmeasured confounders.

Results

Among 431 with PM (59% female, mean age 59.9 years y) and 352 with DM (65% female, mean age 55.7 yeas) the corresponding incidence rate ratio (IRRs)for MI were 8.14 (95% CI; 4.62-13.99) and 3.80 (95% CI; 1.89-7.09) respectively (see table). Overall, the highest IRRs for MI were observed in the first year after PM diagnosis (IRR= 12.65, 95% CI: 5.11-31.65) as well as DM diagnosis (IRR= 6.32, 95% CI; 1.66-21.03). The risk of MI remained statistically significant in the fully adjusted models (hazard ratios= 3.78 (95% CI 2.05-6.95 and 6.54 (95% CI; 2.73-15.67), respectively) (see table). Our results remained statistically significant after adjusting for the potential impact of an unmeasured confounder.

Conclusion

The results of this large truly general population-based study indicates an increased risk of MI in people with PM (four fold) and DM (seven-fold) particularly in the first year after diagnosis, suggesting that inflammation plays a key role in the pathogenesis of MI. Our results support the need for increased monitoring for cardiovascular disease and risk modification to prevent this potentially fatal complication in patients with DM and PM.

* Adjusting for healthcare utilization, medications use (glucocorticoids, hormone replacement therapy (HRT), contraceptives, COX-2 inhibitors, non-steroidal anti-inflammatory drugs), cardiovascular medications (antihypertensives, cardiac glycosides, diuretics, antiarrhythmic, nitrates and anticoagulants), fibrates and statins. In addition, the modified Charlson’s co-morbidity index for administrative data was calculated in the year before the index date.