Use of Proprotein Convertase Subtilisin/Kexin Type 9 Inhibitors in Statin-Associated Immune-Mediated Necrotizing Myopathy: A Case Series

Objective: To determine the safety of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors in patients with statin-associated anti–3-hydroxy-3-methlyglutaryl coenzyme A reductase (anti-HMGCR)–positive immune-mediated necrotizing myopathy (IMNM). Methods: Muscle strength was assessed in anti-HMGCR–positive patients at each visit before and after initiation of PCSK9 inhibitors. The trends in creatine kinase (CK) levels and serum anti-HMGCR antibody titers were monitored over time. Results: Among 122 anti-HMGCR–positive patients, we identified 8 patients who were receiving PCSK9 inhibitors for hyperlipidemia. Patients were followed up for an average of 1.5 years (range 3–37 months), and none exhibited reduction in muscle strength. The mean ± SD CK level prior to the initiation of PCSK9 inhibitors was 956 ± 1,137 IU/liter, which was reduced to 419 ± 393 IU/liter at their last visit. Anti-HMGCR antibody titers followed a similar trend. Notably, in 2 patients, the initiation of the lipid-lowering medication was followed by unanticipated spontaneous clinical improvement and reduction in immunosuppression. Conclusion: PCSK9 inhibitors are safe for long-term use as a cholesterol-lowering agent in patients with statin-associated IMNM.