The Potential Impact of the COVID-19 Pandemic on Clinical Management of Thyroid Disorders in Japan

Background: The indirect influence of the coronavirus disease 2019 (COVID-19) pandemic on clinical practice has received great attention. However, the evidence about how the pandemic has affected clinical management of hypothyroidism and hyperthyroidism, two common diseases worldwide, is lacking. We therefore aimed to examine the trends in the number of outpatients with thyroid disorders and their thyrotropin (TSH) levels before and during the pandemic in Japan. Methods: This cohort study included all patients aged ≥20 years who visited Ito Hospital, one of the largest hospitals that specialize in thyroid disorders in Japan, during 2019/1-2020/6. Our outcomes of interest were 1) trends in the aggregated number of visits at the clinic and 2) trends in average TSH levels from January 2019 to June 2020. The trends in TSH according to the clinic visit in early 2020 were assessed utilizing difference-in-difference models controlling for age, sex, and city of residence, stratified by each medication use (i.e., levothyroxine [LT4], antithyroid drug [ATD], potassium iodine [KI], or no medication). Results: During 2019/1-2020/6, we observed 517,412 visits at Ito Hospital for thyroid disorders, and the average number of visits per month was significantly decreased for both the first visits (1,995 in 2019 vs. 1,268 in 2020; reduction rate, 36%; p<0.001) and the follow-up visits (29,509 in 2019 vs. 21,959 in 2020; reduction rate, 26%; p<0.001). Among 15,455 patients who had been followed in 2019, we found a higher TSH at the follow-up visits during 2020/4-2020/6 among patients with LT4 who did not visit the clinic during 2020/1-2020/3 than those who did (difference-in-difference [95%CI]=+1.77 [1.25-2.29], p<0.001). We also found decreased trends in TSH among patients with ATD or KI who visited the clinic during 2020/1-2020/3 (p<0.001 for both categories), but not among patients with no medications (p=0.29). Conclusions: In this large cohort in Japan, we found the decreased number of outpatients with thyroid disorders since 2020/1 with a nadir in 2020/4. Using individual-level data, we also found the association between visiting the clinic in early 2020 and TSH control at the following visit among patients with medications. These findings highlight the importance of careful monitoring of patients with medications for thyroid disorders during the COVID-19 pandemic.