Statin-associated immune-mediated necrotising myopathy: a New Zealand case series showing possible overrepresentation in Pacific Islanders.

BACKGROUND

Statin-associated immmune-mediated necrotising myopathy (IMNM) is an emerging entity. Being an uncommon condition, our knowledge and understanding is largely based on case series.

AIM: To review incident cases of statin-associated IMNM associated with anti-3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) antibodies in a single New Zealand centre over a 2-year period.

METHODS

Four incident cases of statin-associated IMNM were seen between 2014 and 2016. Their presentation, investigation, treatment and current response to treatment are summarised. Two of the four patients were Pacific Islanders despite a small Pacific Island population in the southern district health board. A literature search was performed focusing on the presentation, investigation and treatment of statin-associated IMNM and also genetic associations with this entity to determine whether Pacific Islanders may be at increased risk

RESULTS

All four patients presented with profound weakness and recent exposure to atorvastatin. All proceeded to muscle biopsy. Two biopsies showed typical IMNM. One biopsy had mild changes, reported as possibly being compatible with anti-HMGCR antibodies. The final biopsy had features consistent with IMNM, with some features suggestive of polymyositis. Two recent studies have shown an association between anti-HMGCR antibodies and the HLA-DRB1*11:01 haplotype. Interestingly, HLA-DRB1 alleles (including HLA-DRB1*11:01) were observed to be among the most frequent alleles in a Pacific Island population study.

CONCLUSION

This is the first case series of statin-associated IMNM with a focus on Pacific Islanders and raises the possibility that Pacific Islanders exposed to statins may be at increased risk of developing an immune-mediated myopathy.