Clinico-serologic features of statin-induced necrotising autoimmune myopathy in a single-centre cohort

Statin-induced necrotising autoimmune myopathy (NAM) is a rare but disabling complication of statin therapy. Data regarding treatment and outcomes in these patients is sparse. We retrospectively identified those patients with a diagnosis of statin-induced NAM who were managed in a single-tertiary referral centre from January 2014 to January 2017. Data regarding clinical features, serology, antibody status and functional outcome was collected. We identified 16 patients diagnosed with statin-induced NAM. Truncal weakness was present in 9/16 patients, of which one patient presented with camptocormia. Following treatment, the mean improvement in the 8-point manual muscle test (MMT8) score was 11 points (range 1-25). Antibodies to 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) were detected in 8/14 patients tested. Of patients who were HMGCR positive, 7/8 had significant truncal weakness, compared with 1/6 who were anti-HMGCR negative. In 4/7 patients who had anti-HMGCR retested following treatment, these antibodies subsequently became undetectable. The disappearance of anti-HMGCR was accompanied by sustained clinical improvement in all four patients. The mean Karnofsky Performance Status (KPS) prior to diagnosis was 89/100, and at latest follow-up had fallen to 68/100. We report a novel association of anti-HMGCR antibodies with truncal weakness in patients with statin-induced NAM. Functional impairments persist despite normalisation of muscle strength. Anti-HMGCR antibodies may disappear with treatment, paralleled by clinical remission of disease. Further prospective clinical trials are needed to determine optimal management strategies for statin-induced NAM.