Painless thyroiditis after mrna vaccination for severe acute respiratory syndrome coronavirus 2 (sars-cov-2)

Thyroid dysfunction has been described following SARS-CoV-2 infection, but data on thyroid dysfunction following SARS-CoV-2 vaccination are extremely limited. We here report the first 3 cases of painless thyroiditis in patients shortly after receiving an mRNA vaccine for SARS-CoV-2. Patient 1: A 39-year-old woman, with history of Hashimoto's disease for 13 years, euthyroid on levothyroxine, presented with palpitations and anxiety about 10 days after receiving the second dose of the mRNA-SARS-CoV-2 Vaccine(Moderna). Labs showed TSH of 0.02 lIU/mL(0.45- 4.5 lIU/mL), free thyroxine(FT4) of 2.95 ng/dL(0.7-1.8 ng/dL), and normal total triiodothyronine (TT3). The patient was asked to hold her levothyroxine and repeat labs 1 week later again showed TSH 0.01 lIU/mL, FT4 2.10 ng/dL and a TT3 107 ng/dL. TSI index was <1.0 and radioactive iodine uptake 2 weeks after stopping thyroid hormone showed near absent uptake of 0.22%. Patient 2: A 47-year-old woman, with a history of thyroid autoimmunity, previously euthyroid on levothyroxine 50 mcg daily, presented with left thyroid lobe painless swelling, paresthesia and join pains 2 weeks after her first dose of mRNA-SARSCoV-2 Vaccine (Moderna), with labs noted for TSH 0.1 lIU/mL and FT4 1.6 ng/dL. Despite reduction in dose, her TSH rose to 21 which returned to normal limits after progressive increase in dose of levothyroxine. Patient 3: A 29-year-old female with history of Graves' disease in remission and off methimazole, now euthyroid on levothyroxine 25 mcg/day for pre-conception optimization, presented with asymptomatic hyperthyroidism after labs drawn five days after her second dose of mRNA-SARS-CoV-2 vaccine(Pfizer) revealed TSH of 0.01 lIU/mL, FT4 of 3.15 ng/dL, TT3 of 162 ng/dL and a negative TSI index. She was asked to hold levothyroxine and labs obtained four weeks later showed normal FT4 and TT3. Awareness about the possibility of thyroiditis in the postvaccination period can help prevent initiation of medical therapy or large adjustments in thyroid medication doses and invites more frequent thyroid testing in patients in whom thyroid dysfunction is suspected.