Statin-associated immune-mediated necrotizing myopathy in Hispanic Americans

Introduction/Objectives: Idiopathic inflammatory myopathies (IIM) are manifested by proximal muscle weakness, inflammation, and elevation of muscle enzymes. Immune-mediated necrotizing myopathy (IMNM) is a form of IIM often associated with anti-3-hydroxy-3-methylglutaryl coenzyme A reductase (anti-HMGCR) antibodies. Recently, certain regional populations have been found to have increased anti-HMGCR antibody IMNM. The present study compared the epidemiology of IIM and IMNM in the adult Hispanic and non-Hispanic Caucasians in the Southwestern USA. Methods: In this retrospective study 97 patients with IIM were self-identified as Hispanic versus non-Hispanic. Statistical comparisons were performed as to prevalence of diabetes mellitus, hyperlipidemia, statin exposure, myopathy diagnosis, muscle histology, autoimmune and myositis-specific autoantibodies, echocardiography, interstitial lung disease, therapy, and outcome. Results: Sixty-two patients self-identified as Hispanic (64 %) and 35 patients as non-Hispanic (36 %). The two groups were similar in terms of baseline characteristics, autoantibody profiles, clinical outcomes, and mortality rates. However, statin-induced anti-HMGCR antibody IMNM was increased in Hispanics (22.6 % versus 5.7 %, OR: 4.81, CI: (1.03, 22.6), p=0.045) as was diabetes mellitus (46.8 % versus 25.7 %, OR: 2.54, CI: (1.02, 6.29), p=0.05). However, there was lesser cancer-associated IIM in Hispanics compared to Non-Hispanics (11.3 % versus 31.4 %, OR: 0.23CI: (0.08, 0.7), p=0.027). Conclusions: Hispanics in the Southwestern USA have increased statin-induced anti-HMGCR antibody IMNM and a lesser prevalence of cancer-associated IIM compared to non-Hispanics. It is uncertain whether these respective differences in statin-induced versus malignancy-associated myositis result from specific genetic and environmental factors, or to greater statin exposure in Hispanics due to increased endemic diabetes mellitus.