HMGCR and myopathy: Based on the type of myositis-specific antibodies (MSAs) involved, IMNM can be further classified as anti–signal recognition particle (SRP) myopathy, anti–3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) myopathy, or seronegative IMNM (1, 4, 5).