How do you decide on initiation of treatment with steroids or immunomodulatory therapy in patients with statin-induced myopathy versus statin-induced autoimmune necrotizing myopathy?

In the setting of limited experience, in patients with statin induced necrotizing polymyositis (HMG-CoA reductase antibody mediated necrotizing myositis), the best approach is typically steroids (prednisone 20mg or so), IViG 2gm/kg every 4 weeks, and potentially CellCept at 2000 to 3000mg per day, with the goal of bringing down the CK over 4 to 12 months. The plan would be to decrease the steroids as able, and increase interval between the IViG doses to space it out.

Biopsy will be the only way to differentiate between necrotizing versus non-necrotizing myositis. I treat patients with positive HmG-COA antibody positivity without biopsy.

In the setting of a hospitalized patient with rhabdomyolysis, the differential between statin toxicity and statin-associated IMNM can be difficult. All diagnostic modalities (muscle biopsy, EMG, muscle MRI) in the acute setting cannot discriminate, so we can only rely on the antibody. Fortunately, this takes only a few days, and in the meantime, could utilize supportive measures (depending on each case).

If the patient has apparent muscle weakness, I give IVIG until the HmG- COA antibody result is back. I avoid steroids as they can be detrimental if it is only rhabdomyolysis.