Background/Purpose: Anti-HMGCR antibodies represent a characteristic serological feature of statin-exposed and statin-unexposed patients with immune mediated necrotizing myopathy (IMNM). We assessed anti-HMGCR antibodies in patients with suspected IMNM following statin exposure and patients with other autoimmune inflammatory diseases.

Methods: We evaluated the presence of anti-HMGCR autoantibodies in sera samples from 13 statin-exposed patients who were suspected of having IMNM, 38 patients with different inflammatory and autoimmune rheumatic diseases (systemic lupus erythematous, rheumatoid arthritis, ankylosing spondylitis, systemic sclerosis, polymyositis and anti-phospholipid syndrome) and 29 healthy subjects. The autoantibodies were detected by two assays: a new chemiluminescence QUANTA Flash HMGCR kit utilizing BIO-FLASH system, and QUANTA Lite^®HMGCR ELISA kit.

Results: Twelve samples from patients with suspicion for IMNM were found positive for anti-HMGCR antibodies by both assays. Only one of the 13 samples that were found positive by QUANTA Flash HMGCR was negative by QUANTA Lite® HMGCR. A very good qualitative agreement was found between these two assays (kappa=0.949; P value < 0.0001; 95% CI, 0.918 – 1.0). A quantitative comparison between QUANTA Flash HMGCR and QUANTA Lite® HMGCR based on the levels of anti-HMGCR antibodies also revealed a strong correlation (Spearman’s coefficient 0.846; 95% CI, 0.686 -0.928). In statin-exposed patients, the diagnosis of necrotizing myopathy was proven by muscle biopsy (10 patients underwent biopsy before and 3 patients after the detection of anti HMGCR antibodies). All samples from healthy subjects and from the disease-controlled patient cohort were negative for anti-HMGCR antibodies. Receiver operating characteristic (ROC) analysis for QUANTA Flash and QUANTA Lite® yielded area under the curve values of 0.997 and 1.0 respectively. The sensitivity and specificity for IMNM were 100% and 100% for ELISA and 100% and 96.3% for CIA resulting in odds ratios of 1593 and 491.2 correspondingly.

Conclusion: The presence of anti-HMGCR antibodies is a useful biomarker of IMNM in statin-exposed patients. There is a good correlation between the two anti-HMGCR antibody assays evaluated in the present study.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/anti-hmgcr-antibodies-demonstrate-high-diagnostic-value-in-the-diagnosis-of-immune-mediated-necrotizing-myopathy-following-statin-exposure/