A Comparative Analysis of Subacute Thyroiditis: Before and After COVID-19.

OBJECTIVE

The COVID-19 infection impacts endocrine tissues, and various thyroid disorders have been reported in affected patients. Subacute thyroiditis (SAT), a self-limited inflammatory thyroid condition, is associated with viral respiratory tract infections. Studies have suggested a link between COVID-19 and SAT. Our study expands on this by examining differences in SAT severity before and after COVID-19.

METHODS

A retrospective cohort study analyzed SAT cases at an outpatient Ontario endocrinology clinic. Cases were identified as pre-Covid (December 2015 - April 2019) or post-Covid (December 2019 - April 2023). Patient charts were screened for diagnostic characteristics of SAT and relevant lab data, including thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3). From 436 pre-Covid and 629 post-Covid cases, 32 and 37 met the inclusion criteria.

RESULTS

Our study showed no difference between incidence of SAT cases post-Covid versus pre-Covid. However, post-Covid, more patients had severe SAT, defined as values of FT4 and FT3 >30% above their upper normal range and TSH >10, (FT4 37.8 ∓ 6.7 vs 50.9 ∓ 23.5 [P = 0.05]; FT3 9.6 ∓ 2.2 vs 18.6 ∓ 10.9 [P = 0.02]). No significant differences were identified in median TSH levels during hyperthyroid phase (P = 0.12). In the hypothyroid phase, median TSH values were significantly higher post-Covid (P = 0.0046). Low FT4 values also showed significance (P = 0.001).

CONCLUSION

Our study shows SAT incidence was similar pre- and post-COVID-19. Severity of the SAT disease course was amplified after the onset of the COVID-19 pandemic, with a significant elevation in FT4 and FT3 levels during hyperthyroidism and higher TSH during hypothyroidism in the post-Covid cohort.