A diagnosis of immune-mediated necrotizing myopathy associated with these two antibodies was made. We started 50 mg a day of prednisolone orally, as well as cessation of mushroom intake. His symptoms and CK levels quickly improved. We tapered the prednisolone and started azathioprine. Although we discontinued azathioprine because of side effects, his symptoms remained stable. Eighteen months later, we successfully discontinued prednisolone and are now observing his symptoms without treatment.
In East Asia, the rate of statin-naive, anti-HMGCR antibody-positive immune-mediated necrotizing myopathy is much higher than in North America, raising a possibility that different triggering materials may be associated with immune-mediated necrotizing myopathy.
Statins are believed to trigger autoantibody production against HMGCR in individuals who have a susceptibility.8 Regenerating fibers are known to overexpress HMGCR. Therefore, statin-induced myofiber necrosis and generation may well provide more antigens to produce pathogenic autoantibodies, creating a feed-forward loop.2,7 The binding of statins to HMGCR may also change the conformation of the protein, leading to the generation of new epitopes to which the immune system is not tolerant.2