Increased prevalence and incidence of statin-associated immune-mediated necrotizing myopathy in Native Americans

Statin-associated immune-mediated necrotizing myopathy (IMNM) is an idiopathic inflammatory myopathy (IIM) associated with anti-3-hydroxy-3-methylglutaryl coenzyme A reductase (anti-HMGCR) antibodies. This research determined the characteristics and outcomes of Native Americans vs non-Native Americans (non-NA) diagnosed with IIM and IMNM from the American Southwest.

In this retrospective single-institution study, IIM diagnosis was established with standard criteria, and statin-associated IMNM diagnosis required the presence of anti-HMGCR antibodies. Of 148 subjects with IIM, 33 self-identified as Native American and 115 as non-NA. The proportion of IIM and IMNM in each group, clinical and laboratory parameters, and the outcomes were compared.

Compared with non-NA, Native Americans with IIM had a lower body mass index, myositis damage index and inflammatory arthritis, but more hyperlipidemia (75% vs 49.6%; P = 0.015), statin exposure (71.9% vs 40.0%; P = 0.002), diabetes mellitus (DM) (62.5% vs 34.8%; P = 0.044) and esophageal dysmotility (93.8% vs 77.4%; P = 0.042). Native Americans more frequently expressed anti-RNP antibody (15.6% vs 2.6%, P = 0.013) and anti-HMGCR antibody (46.9% vs 16.5%, P = 0.0007). The estimated prevalence of statin-associated IMNM in Native Americans vs non-NA was 182 vs 30.6 cases/106 population, and incidence was 66.4 vs 7.5 cases/year/106 population. There were no significant differences in the clinical outcomes and treatment received between the two groups.

Statin-associated IMNM is significantly more common in Native Americans in the American Southwest. The treatments received and outcomes of statin-associated IMNM in Native Americans and non-NA seem to be similar. The underlying genetic and environmental factors predisposing to IMNM in these populations require further study.