Idiopathic inflammatory myopathies (IIM) are heterogeneous autoimmune diseases characterized by chronic muscle inflammation. Conversely to systemic lupus erythematosus, thrombocytopenia is rare in IIM. In this study we collected the clinical features of IIM patients with thrombocytopenia, and analyzed the possible prognostic indicators, in order to effectively guide better treatment and judge the clinical outcome for these IIM patients. 

132 cases of IIM patients from January 1, 2019 to December 31, 2025 in Nanjing Drum Tower Hospital and Wuxi People's Hospital were included for our study. The clinical manifestations, hematological makers, complications and outcomes of IIM patients associated with thrombocytopenia were all collected. These data were analyzed for the possible prognostic indicators to guide a better management.

IIM patients (n=132) with thrombocytopenia in our cohort comprised of 23 patients with ASS (17.4%), 91 patients with DM (68.9%) and 18 cases with PM (13.6%). The mortality rates were significantly higher in patients with DM (42.5%, p<0.05) and PM patients (33.3%, p<0.05) than those of ASS patients (13.0%). These patients displayed increased mortality when accompanied by fever (p<0.01), and involving in lung (p<0.01), CNS (p<0.01), kidney (p<0.01) and heart (p<0.05), especially platelets not restored (p<0.001). IIM patients with cancer showed elevated mortality rates compared to those without cancer (p<0.05).

The platelet counts were evidently reduced in patients who eventually died compared to those of survival patients (p<0.05). Positive antibodies of anti-MDA5 and anti-SRP were associated with increased mortality of IIM patients, as well as higher levels of CRP, ESR and triglyceride (p<0.05). We also observed more percentages of CD19+ B cells in the death group patients.

Several clinical factors associated with increased risks of mortality of IIM patients, included cancer (p=0.025), fever (p=0.003), lung (p=0.011), central nervous system (p=0.016), kidney (p=0.003) and heart (p=0.029). Methylprednisolone (p=0.023), IVIG (p=0.003) seems to be correlated with the poor prognosis in IIM patients with thrombocytopenia, due to the fact that we tended to choose higher doses of glucocorticoid and IVIG in these more worse patients.

Multivariate analysis confirmed that independent risk factors of mortality for IIM patients with thrombocytopenia included fever (p<0.01), kidney involvement (p<0.01) and platelets cannot be restored (p<0.001), however, longer internal time from IIM diagnosis (p<0.05) may be a weak protective fact for these patients.

In conclusion, fever, and kidney involvement are independent risk factors for poor prognosis of IIM patients with thrombocytopenia. In particular, these patients whose platelet counts could not return to the normal range displayed a significantly increased mortality. Therefore we should pay more attention to these IIM patients with thrombocytopenia in clinical practices.