Disease activity and immune disbalance are key drivers of infections in patients with idiopathic inflammatory myopathies: results from the MYOTReCSZ cohort.

Patients with idiopathic inflammatory myopathies (IIM) are at increased risk for infections. Identifying clinical and immunological biomarkers predictive of infection is essential. We included 169 patients from the MYOTReCSZ cohort, all with ≥ 6 months of follow-up. Clinical data and laboratory parameters were collected, including: (1) low-density granulocytes and monocyte subsets, (2) serum cytokines, and (3) neutrophil extracellular trap (NET) quantification. The primary outcome was infection development. Most patients were female (72.78%), with a median age of 42. At least one infection occurred in 46.7% of patients; 55.6% were severe and 32.9% had recurrent infections. Independent predictors of infection included number of immunosuppressants (OR 1.7, P = 0.023), gastrointestinal activity score, cardiovascular damage-VAS, anti-Jo1 positivity (OR 10.0, P = 0.05), heliotrope rash, alopecia, and mycophenolate mofetil use (OR 11.9, P = 0.026). Severe infections were associated with number of immunosuppressants, low albumin, constitutional activity score, gastrointestinal damage-VAS, and TLR4⁺ intermediate monocytes (OR 1.0, P = 0.038). Recurrent infections correlated with lower TLR2⁺ classical monocytes (OR 0.4, P = 0.045), cumulative prednisone dose, global damage-VAS (OR 2.0, P = 0.0004), and anti-PM/Scl75 positivity (OR 3.8, P = 0.006). In conclusion, IIM patients with higher baseline activity and damage scores, specific autoantibodies, and altered innate immune cell phenotypes are more likely to develop infections. These parameters may serve as early biomarkers to stratify infection risk in clinical practice.