Statin-induced myositis: less rare than we thought?

5 minute read

An Adelaide rheumatologist presented his findings from a multi-site cohort study at the combined NZRA and ARA ASM in New Zealand.

Statin-induced anti-HMGCR immune necrotising myositis may be more common than previously thought, the combined New Zealand Rheumatology Association (NZRA) and Australian Rheumatology Association (ARA) Annual Scientific Meeting has heard.

Dr Thomas Khoo, a rheumatologist and University of Adelaide PhD candidate, presented results from an Australian and UK nationwide retrospective multi-site cohort study at the ASM in Christchurch on Sunday.

The results follow on from a paper co-authored by Dr Khoo and published in Autoimmunity Reviews in December, which described the discovery of anti-HMGCR in 2010 as a “major step forward in identifying a new subgroup of patients with IMNM who were negative for the anti-SRP autoantibody”.

“However, beyond this contribution to classification, anti-HMGCR has a unique status among the MSA in being strongly associated with an acquired risk factor, statin therapy,” the authors concluded.

“Although rare, anti-HMGCR has the potential to provide a conceptual paradigm of genetic and environmental interactions that can be translated to other subtypes of IIM.

“There remain unanswered questions surrounding anti-HMGCR. Phenotypic, histopathological and ethnic heterogeneity in anti-HMGCR is being increasingly recognised. The pathogenesis and patterns of disease in juvenile patients, statin-naïve adults and patients with a chronic limb girdle muscular dystrophy-like presentation need further exploration in isolation but also for the potential links that might unite these sub-groups.”

Dr Khoo recently completed an international clinical and research fellowship with Salford Royal Hospital and the Manchester Myositis Research Group in the UK, supported by the Arthritis Australia/ARA Ken Muirden Overseas Training Fellowship.

The cohort study he presented on at the ASM was part of were conducted during his time in the UK.

“We have four sites from Manchester, as well as Bristol, South Australia and Western Australia,” he explained to Rheumatology Republic this week.

“And overall, we have 95 patients from that, which is a really large cohort of anti-HMGCR patients across two countries, which hasn’t been done before. Our main goals were to try and calculate an incidence to see if it is as low as it was when it was first described in 2010, or if it’s higher, and then also to describe the characteristics of this disease.

“Are they still as they were described when it was first reported 14 years ago, or do we understand a bit better now in terms of how it presents and how it responds to treatment?”

According to Dr Khoo’s previous paper, initial studies from the Johns Hopkins Myositis Centre reported an incidence of two cases per million per year and 25 cases per million statin users per year. Other studies reported similar incidences, such as 1.7 per million in New Zealand (2014-15) and 0.9 to 2.4 per million in regions of the UK and Australia (2018-22).

Dr Khoo told the ASM that the incidence was “probably a bit more common than we think it is”.

“We have an incidence of about 2.5 per million per year, which doesn’t sound like much, but it’s more than what was thought previously, and it’s also a difficult condition to treat,” he told RR.

Of the 95 patients in his recent study, less than half of them at followup had improved back to normal, and about half of them were still taking steroids, he said.

“So it’s definitely a tricky myositis to get managed,” he said, adding that simply stopping the statins was not the answer.

“The statin ignites the immune system, and even after you stop the statin, things just keep burning along.”

Dr Khoo said picking the myositis up early gave patients the best chance of avoiding severe disease and a faster recovery. And this was where clinicians could make a difference, despite its rarity.

“I think that anyone who’s been on statins for any period of time who develops weakness or a raised muscle enzyme, or CK [creatine kinase], which doesn’t get better, or doesn’t get better as quickly as you’d expect when you take the statin away, should be tested for this antibody,” he said.

“I think there’s a lot of cases where there’s a lot of delay, a watch and wait to see if off the statin these patients get better completely. But I think trying to test for this antibody more readily is a good idea.”

This might present challenges for clinicians, as not all laboratories test for it. Anti-HMGCR testing, typically done via ELISA, was not included in common line blot immunoassays, leading to potential underdiagnosis.

Treatment of anti-HMGCR IMNM generally involves immunosuppressive therapies, and intravenous immunoglobulin (IVIG) has shown efficacy in managing the condition. However, treatment responses can vary, and some patients may experience refractory disease despite multimodal immunosuppression, Dr Khoo said.

“The earlier you treat people, the less likely they are to need extensive rehabilitation and the more likely they are to get back to normal muscle power,” he said.

“The longer you leave it, the more these patients’ muscles atrophy away, and the harder the journey just to get back to normal.”

The study results have been submitted for publication, Dr Khoo told RR. However, there was still much more research to be done, including whether patients with the disease could safely continue to take statins if absolutely needed.

“We don’t have the data to say that they have to be stopped,” he said.

“We all do it because it makes sense. But actually, no one’s really studied a group of patients which haven’t stopped their statins. All of the patients in my cohort stopped their statins because that is currently the sort of standard of care.

“But it would be good to get more research, firstly, on, do patients have to stop statins? And secondly, is it safe to put these patients back on a different statin?

“Again, none of us do that because we all are fearful. But there’s no evidence to say that you can’t try that.”

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