OBJECTIVES To investigate immune-mediated necrotizing myopathy (IMNM) association with cancer and its clinical implications. METHODS IMNM cases were identified January 1st, 2000 to December 31st, 2020 matching sex and age… Click to show full abstract
OBJECTIVES To investigate immune-mediated necrotizing myopathy (IMNM) association with cancer and its clinical implications. METHODS IMNM cases were identified January 1st, 2000 to December 31st, 2020 matching sex and age controls (4:1). RESULTS 152 patients with IMNM were identified and among serologically tested, 60% (83/140) were HMGCR-IgG+, 14% (20/140) were SRP-IgG+ and 26% (37/140) were seronegative. Cancer rates were not significantly different between serological subgroups; 18.1% (15/83) HMGCR-IgG+, 25% (5/20) SRP-IgG+ and 30% (11/37) seronegative (p= 0.34). Cancer screening was performed within 12 months from IMNM diagnosis in 88% (134/152) (whole-body CT plus FDG-PET CT in 53, CT alone in 72 and FDG-PET alone in 9). FDG-PET/CT was positive in 73% (25/34) of cancers. Increasing age was the only risk associated with cancer (p= 0.02). The odds of developing cancer at ± 3 or ± 5 years from IMNM diagnosis was not higher than controls (OR = 0.49; CI : 0.325-0.76). Lifetime IMNM diagnosis of cancer was less compared with controls (OR = 0.5 CI: 0.33-0.78, p= 0.002). Most patients responded to treatment (137/147, p< 0.001). Death and treatment response did not significantly differ between cancer [23% (8/34); 88% (29/33)] and non-cancer patients [19% (23/118); 92% (108/118)]. 13% (20/152) of patients died during follow-up compared with 14% (41/290) of medicine and 16% (46/290) of neurology controls (p= 0.8). Seropositives had greater life expectancy than seronegatives (p= 0.01). CONCLUSIONS Greater cancer risk is not observed in IMNM vs controls. Cancer screening in IMNM should be individualized based on age-personal and family history, including consideration of FDG-PET/CT. Immune-treatment response did not differ with cancer.
               
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