Frequency of Thyroid Antibodies at the Diagnosis of Subacute Thyroiditis

Abstract

Objective: Although subacute thyroiditis (SAT) is not an autoimmune disease, the presence of antithyroid antibodies has been reported in this disease too. This study aims to determine the frequency of antithyroid antibodies at the time of diagnosis of SAT. Material and Methods: Quantitative measurements of antithyroid peroxidase antibody (anti-TPO), antithyroglobulin antibody (anti-Tg), and thyroid-stimulating hormone (TSH) receptor autoantibodies (TRAb) were made in 76 patients at the diagnosis of SAT. Cytopathological examination and iodine uptake test was performed to exclude Graves' disease and Hashimoto's disease in suspected patients. Multiple multinuclear giant cells and granulomatous formations, including epithelioid histiocytes, were the cytological findings employed to support the diagnosis of SAT in suspicious cases. Results: The median erythrocyte sedimentation rate and Creactive protein levels were found to be 49 mL/hour (21-130) and 54 mg/L (8-179), respectively. TSH, free T4, and free T3 levels were determined to be 0.01 mIU/L (0.003-5.2), 1.98 ng/dL (0.78-6.1) and 5.51 ng/L (3.07-14), respectively. During the initial presentation, 88% of the patients were hyperthyroid, and 9% of the patients were euthyroid. Anti-TPO and anti-Tg antibody levels were detected to be above the assay-specific cutoff in 11.8% and 10.5% of SAT patients, respectively, at the time of diagnosis. Elevated TRAb was detected in 6.6% of all SAT patients. The median anti-TPO, anti-Tg, and TRAb levels of antibody-positive patients were 55 IU/mL (38-1.078), 163 IU/mL (5.5-876), 5 IU/L (1.9-23), respectively. Conclusion: Although uncommon, antibody positivity can also be observed in SAT disease. This study has proved that the previous studies claiming the absence of thyroid antibodies in SAT are flawed. SAT must be considered while assessing the differential diagnosis of Graves' and Hashimoto's disease.

Differences in Clinical Aspects Between Subacute Thyroiditis Associated with COVID-19 Vaccines and Classical Subacute Thyroiditis

“…Analysis of a large population of classical SAT revealed that the frequency of positivity of ATPO was found as 7.8% 32 . In another study, it was found a little bit higher as 11.8% 33 . We could not measure thyroid autoantibodies in all patients, but at least one of them was positive in approximately one fifth of the patients in Vac-SAT, and no difference was found among the groups.…”

fT3 index/TSH index ratio and free thyroid hormone index in the differential diagnosis of thyrotoxicosis

“…In such scintigraphic limitations, TSH receptor antibodies are helpful in distinguishing GD from other conditions. However, there may be false-negative and false-positive results (8,9). A total T3/total T4 ratio of <20 ng/mcg in thyrotoxic patients is considered an indicator of destructive thyrotoxicosis (7).…”