Background/Purpose:  Statin-induced autoimmune myopathy (SI-AIM) is often difficult to treat. While corticosteroids (CSs) are the mainstay induction therapy used by most clinicians for autoimmune myopathies, SI-AIM seems corticosteroid resistant. Intravenous immune globulin (IVIG) on the other hand has been used with success as part of an induction regimen or even as monotherapy (Mammen AL, NEJM, 2015). Our objective was to describe the clinical phenotype and successful treatment regimens of patients with SI-AIM but not treated with CSs.

Methods:  Our study included all patients from the Université de Montréal AIM cohort (comprising four academic hospitals) with a documented anti-3-hydroxy-3-methylglutaryl-CoA reductase (anti-HMGCR) autoantibody. We selected statin-exposed patients who did not receive any CSs during the course of their treatment and performed a retrospective review of medical records. Remission was defined as a serum creatine kinase (CK) level <500 U/L whereas maintenance of remission corresponded to a CK level <500 U/L sustained for at least 6 months.

Results:  From a cohort of 45 anti-HMGCR positive AIM patients, 42 were previously exposed to statins, of whom 8 patients (4 men, 4 women, mean age 59 years) were not treated with CSs and therefore selected for study. Three clinical stages of myopathy were recognized: stage 1 (serum CK elevation, normal muscle strength, normal EMG), stage 2 (CK elevation, normal strength, myopathic EMG) and stage 3 myopathy (CK elevation, proximal muscle weakness, myopathic EMG). Three out of 8 patients presented and were treated in stage 1 myopathy after a mean statin discontinuation time of 23 months (range 5-74 months). The remaining 5/8 patients presented in stage 3 myopathy. The mean time between statin cessation and treatment initiation was 5 months (range 0-10 months), with one patient improving to stage 2 myopathy upon statin discontinuation. MTX monotherapy induced remission in all 3 patients presenting in stage 1 myopathy and in 1 patient in stage 2 myopathy. The mean time to remission was 7 months (range 4-13 months). In the remaining 4 patients with stage 3 myopathy, IVIG was successfully used in 3 patients to induce remission with either MTX or MTX+AZA, whereas 1 patient responded to a MTX+AZA combination alone. The mean time to remission for stage 3 myopathy was 10 months (range 1-21 months). MTX monotherapy (n=5/6) or a MTX+AZA combination (n=1) were able to maintain remission in the 6 patients available for analysis. Thus, all 8 patients did not require CSs to achieve remission.

Conclusion:  Eight patients with SI-AIM were successfully treated with immunosuppressive and/or immunomodulating agents but not with CSs. Four patients with normal strength (i.e. in stage 1 or 2) responded to MTX monotherapy. In patients with proximal muscle weakness, combination therapies with MTX+IVIG, MTX+AZA or MTX+AZA+IVIG were successfully used and thus, these approaches appear reasonable induction strategies in stage 3. Early recognition of stage 1 SI-AIM and timely treatment initiation could minimize the use of IVIG and CS therapies and consequently lead to better outcomes in these patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/successful-treatment-of-statin-induced-autoimmune-myopathy-without-corticosteroids/