Immune checkpoint inhibitor-induced myositis, the earliest and most lethal complication among rheumatic and musculoskeletal toxicities

Background: In addition to restoring anti-tumor immune responses, immune checkpoint inhibitors (ICI) may also induce immune-related adverse events (irAE) that can affect any organ. We aim to determine the spectrum, timing, clinical features, and fatalities of rheumatic and musculoskeletal immune-related adverse events (RMSirAE) associated with ICI. Patients Methods: We performed an observational, retrospective, pharmacovigilance study using the World Health Organization international pharmacovigilance database, VigiBase, from inception to January 2019. RMSirAE reporting rate on ICI versus full database was performed using disproportionality analysis with computation of reporting-odds-ratios (ROR) and a Bayesian disproportional estimate (information component, IC). IC025 (lower end of the IC 95% credibility interval) > 0 is deemed significant. Results: We identified 1288 RMS-irAE significantly associated with ICI: polymyalgia rheumatica (n = 76, ROR = 14.6 [11.6-18.4], IC025 = 3.34), sarcoidosis (n = 94; ROR = 9.6 [7.9-11.9]; IC025 = 2.85), Sjogren's syndrome (n = 49; ROR = 6.9 [5.2-9.2]; IC025 = 2.24), myositis (n = 465; ROR = 4.9 [4.5-5.4]; IC025 = 2.12), arthritis (n = 606; ROR = 1.4 [1.3-1.5]; IC025 = 0.34) and scleroderma (n = 17; ROR = 2.0 [1.2-3.2]; IC025 = 0.17). Arthritis, myositis, and Sjogren's syndrome were over-reported in patients treated with ICI combination versus those treated with ICI monotherapy (ROR = 1.6-2.9, p < .05) and more frequently reported on anti-PD1/PDL1 monotherapy vs. anti-CTLA4 monotherapy (2.1-4.4, p < .05). Median time to onset occurred early for myositis (31 days [19.2-57.8]) and was the most delayed for scleroderma (395 days [323.8-457.2], p < .0001). The fatality rate for RMS-irAE ranged from 24% for myositis (n = 106/441) (up to 56.7% with concurrent myocarditis) to [0-6.7%] for other RMS-irAE (p < .0001). Conclusions: Clinicians should be aware of the spectrum of RMS-irAE. Myositis can be particularly life-threatening, particularly when associated with myocarditis.