To understand the characteristics of Korean patients with anti-HMGCR myopathy, we measured anti-HMGCR antibodies and analyzed clinical, radiological, and pathological features. 

Immune-mediated necrotizing myopathy (IMNM) is an inflammatory myopathy subgroup characterized by subacute proximal weakness and prominent myofiber necrosis with minimal inflammatory cell infiltrate on muscle biopsy. Two autoantibodies have been reported in association with IMNM: antibodies against the signal recognition particle (SRP) and 3-hydroxy-3-methylglutaryl-coenxyme A reductase (HMGCR). To date, there only have been two case reports of Korea patients with anti-HMGCR myopathy. 

We measured titers of anti-HMGCR antibodies in the sera of 99 patients with inflammatory myopathy using the enzyme-linked immunosorbent assay. We also tested 16 myositis-specific autoantibodies (MSAs) in all patients with anti-HMGCR myopathy.

Postivity for the anti-HMGCR antibody was observed in 17 (4 males and 13 females) of 99 patients with inflammatory myopathy.  The median age at symptom onset was 60 years. Ten (59%) of the anti-HMGCR positive patients had taken statins. The most common symptoms were proximal muscle weakness in 15 (88%), followed by myalgia in 9 (53%), neck weakness in 4 (24%), dysphagia in 3 (18%), and skin lesions in 2 (12%). The median titer of anti-HMGCR antibody was 202 U/ml. We found eight different MSAs in nine (53%) patients. The median disease duration from symptom onset to diagnosis was significantly shorter in the MSA-positive group than in the MSA-negative group (p = 0.027).

In conclusion, our study is the first to measure anti-HMGCR antibodies with inflammatory myopathy, and identify new findings including the coexistence of other MSAs in Korean patients.