Objectives
Statin-associated immune-mediated necrotizing myopathy (IMNM) and idiopathic inflammatory myositis (IIM) are myopathies with overlapping features. This study compared the manifestations of IMNM to IIM in Native Americans.
Method
Twenty-one Native American patients with inflammatory myopathy (IM) were characterized as to diabetes mellitus, hyperlipidemia, statin exposure, myopathy diagnosis, muscle histology, autoimmune and myositis-specific autoantibodies, therapy, and outcome.
Results
IM consisted of 52.4% IMNM, 42.9% IIM, and 4.8% metabolic myopathy. IMNM vs. IIM had greater age (61.6±9.8 vs. 39.8±14.3 years), diabetes mellitus (100% vs. 55.6%), hyperlipidemia (100% vs. 33.3%), statin-exposure (100% vs. 22.2%), creatine kinase (CK) (11,780±7064 vs.1707±1658 IU), anti-HMG CoA reductase (anti-HMG CoA) antibodies (85.7% vs. 11.1%), and necrotizing IM (81.8% vs. 11.1%), but lesser disease duration (26.2±395 vs. 78.4±47.9 months), Raynaud’s phenomenon (9.1% vs. 55.6%), cutaneous manifestations (0% vs. 55.6%), antinuclear antibodies (18.2% vs. 66.7%), or any autoantibody (18.2% vs. 88.9%) (all p < 0.05). Magnetic resonance abnormalities, histologic IM, myositis-specific autoantibodies, pulmonary hypertension, esophageal dysfunction, interstitial lung disease, disability, and persistently elevated CK were similar. IMNM vs. IIM was treated more with intravenous immunoglobulin (72.7% vs. 11.1%, p = 0.009) and less with antimetabolites (45.5% vs. 88.9%, p = 0.05) and rituximab (18.2% vs. 55.6%, p = 0.09).
Conclusions
IMNM may occur in Native Americans and is associated with diabetes mellitus, hyperlipidemia, statin use, and older ages, and characterized by marked CK elevation, necrotizing myopathy, and anti-HMGCoA antibodies with few cutaneous or vascular manifestations.
