Anti-HMGCR myopathy: observed ethnic differences in disease and disease outcomes in New Zealand

Objectives Anti-HMGCR myopathy is an immune-mediated necrotizing myopathy strongly associated with statin use in adults. Polynesians have a higher incidence of anti-HMGCR myopathy in New Zealand (NZ), but ethnic differences in phenotype and outcome are not known. Methods 91 patients with anti-HMGCR myopathy were identified based on anti-HMGCR positivity by immunoprecipitation assay. Prioritised ethnicity data was used to identify 35 Polynesian and 48 NZ European patients to include in the cohort. Clinical records were accessed and information on disease phenotype, treatment, and outcome was obtained. Results Polynesian patients were younger than NZ European patients at presentation (median 64 vs 71 years p= 0.009). They were less likely to normalize their CK over the follow-up period (54.2% vs 79.2%, p= 0.016), even after controlling for length of follow-up. There were no other significant differences in disease phenotype or outcome found. Conclusion In addition to having higher incidence of anti-HMGCR myopathy, Polynesians are affected at a younger age and are less likely to achieve normal CK levels despite treatment over similar follow-up periods. The disproportionate burden of disease in this group should prompt early assessment of a Polynesian patient who presents with muscle symptoms while on a statin.