Statin-Associated Late-Onset Anti-HMGCR-Induced Immune-Mediated Necrotizing Myopathy in a 93-Year-Old Woman: A Case Report

Immune-mediated necrotizing myopathy (IMNM) is an exceptionally uncommon variant of idiopathic inflammatory myopathies (IIMs). Statins have been linked to a range of muscle-related side effects described as statin-associated muscle symptoms (SAMS), including IMNM, which is triggered by anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies. We present a case involving a 93-year-old woman who had been using statins for over two decades and exhibited progressive muscle weakness, predominantly proximal rather than distal, along with elevated serum creatine kinase levels, notable denervation on electromyography, and myopathic motor unit action potentials, leading to her diagnosis of anti-HMGCR-induced IMNM. Her condition was extremely severe, rendering her completely dependent on others and confined to bed. Throughout her illness, she underwent treatment with glucocorticoids, intravenous immunoglobulin (IVIG), mycophenolate mofetil (MMF), and a low-dose induction of rituximab (RTX). Additionally, she was diagnosed with subclinical hypothyroidism, which may have contributed to her heightened susceptibility to statin-induced IMNM. She developed severe pneumonia and a urinary tract infection, along with septic shock, after being off immunosuppressive medications for about two months following a low-dose rituximab infusion. Unfortunately, she passed away before the minimum expected duration for meaningful recovery had elapsed. This case underscores the necessity of considering anti-HMGCR-induced IMNM in patients who are using statins. Reporting this uncommonly observed, very late-onset, and rare SAMS aims to enhance awareness among healthcare providers treating individuals with dyslipidemia and other atherosclerotic conditions who require statin therapy.