Statin associated necrotizing autoimmune myopathies in the Indigenous population: a case series from North Queensland

Aim: To describe clinical and histopathological features of statin associated necrotizing autoimmune myopathies (NAM) in Indigenous Australians and increase awareness of this condition amongst treating physicians. Methods: Cases were collected through the Rheumatology Department at The Townsville Hospital between March 2012 and January 2015. A chart review was performed to obtain retrospective information about each case. We detail patient demographics, presenting features, histopathological findings, autoimmune profile, treatment and outcomes. Results: 4 Indigenous Australians were identified as having a biopsy confirmed statin associated NAM. All patients had been on atorvastatin for at least 2 years and had significant proximal weakness with average CK level on presentation 16,820 U/L. Predisposing factors for myopathy included vitamin D deficiency and diabetes mellitus (all cases), with primary hypothyroidism and liver cirrhosis identified in two other cases. Two individuals were positive for the auto-antibody anti-HMGCR. Histopathological findings included muscle necrosis with varying degrees of inflammation, membrane attack complex (MAC) deposition and MHC-1 upregulation. Treatment involved various combinations of prednisolone, IVIG, methotrexate and mycophenolate. Recovery was slow but favourable in all cases with an average length of inpatient stay of 54 days. There was a significant delay in diagnosis of 1–3 months in two of the cases. Conclusions: The statin associated necrotizing autoimmune myopathies are rare but important disorders that cause significant morbidity to affected individuals. Given the prevalence of cardiovascular disease in Indigenous Australians, further research is required to facilitate earlier diagnosis and improved treatment outcomes