Could the Systemic Immune Inflammation Index Predict Diagnosis, Recovery Time, Hypothyroidism, and Recurrence Rates in Subacute Thyroiditis?

PURPOSE: Subacute thyroiditis (SAT) is a non-infectious inflammatory disease of the thyroid. The Systemic Immune-Inflammation Index (SII), also known as an easy economical marker, correlates with the severity of inflammatory responses. We aimed to evaluate the clinical significance of the SII and to compare it to other inflammatory markers in terms of diagnosis, recovery time, and recurrence of SAT. PATIENTS AND METHODS: The current non-interventional observational prospective study was performed at Outpatient Department of Endocrinology, Erzurum Training and Research Hospital. Sixty-nine patients with SAT and fifty-nine healthy individuals in total were enrolled in our study. The follow-up period was 6–12 months for all patients regarding treatment response, recurrence, and hypothyroidism. RESULTS: The SII level was found to be significantly higher at the time of diagnosis in the SAT group compared to the control group (p=0.000). There was a significant positive correlation between the SII and SAT recovery time (p=0.000), particularly in patients receiving methyl prednisolone treatment (p=0.002). SII was not found to be significantly associated with hypothyroidism and recurrence in patients with SAT (p=0.261, p=0.568). However, compared to the ones without recurrence, thyroid stimulating hormone (TSH) and erythrocyte sedimentation rate levels at the time of diagnosis were found to be higher in those patients with recurrence (p=0.035, p=0.046). CONCLUSION: SII is a low-cost, widely available, universal indicator of inflammatory processes in SAT. It could provide many benefits in the follow-up process and the selection of aggressive anti-inflammatory treatment by estimating recovery time. SII, as a practical biomarker, may be a new diagnostic and prognostic tool for SAT.