Value of the Inflammatory Burden Index in the Diagnosis and Prognosis of Subacute Thyroiditis

This study sought to assess the utility of the inflammatory burden index (IBI) in differentiating subacute thyroiditis (SAT) from Graves' disease (GD) and to investigate its association with recovery time, hepatic function impairment, recurrence, and permanent hypothyroidism in patients with SAT.

Clinical and laboratory data from 357 adult patients with SAT, 412 patients with GD, and 633 healthy controls were retrospectively analyzed. Determinants influencing recovery time, hepatic function impairment, recurrence, and permanent hypothyroidism in patients with SAT were systematically evaluated.

The IBI in the SAT cohort was markedly higher than that observed in both patients with GD and healthy controls. Receiver operating characteristic curve analysis indicated that the optimal IBI cutoff value for distinguishing SAT from GD was 9.13, yielding a diagnostic sensitivity of 90.76%, a specificity of 88.35%, and an area under the curve (AUC) of 0.944 (95% confidence interval, 0.927 to 0.961). The AUC for IBI was markedly superior to those for erythrocyte sedimentation rate (ESR), C-reactive protein, systemic immune-inflammation index, and other complete blood count-derived indices. Among patients with painless SAT, the IBI was markedly elevated compared with that in thyroid-stimulating hormone receptor antibody (TRAb)-negative GD patients. Stepwise multiple logistic regression identified ESR, IBI, free thyroxine, and thyroid-stimulating hormone as independent predictive factors for SAT. IBI was not associated with recovery time in patients with SAT. However, higher IBI values were observed in patients requiring glucocorticoid therapy due to an insufficient response to non-steroidal anti-inflammatory drugs. Furthermore, no significant associations were identified between IBI and hepatic function impairment, recurrence, or permanent hypothyroidism in patients with SAT.

IBI, as a simple and practical inflammatory biomarker, could potentially serve as a valuable diagnostic tool for differentiating SAT, particularly in diagnostically challenging cases. Moreover, it may have clinical relevance in guiding therapeutic decision- making for patients with SAT.