Painless thyroiditis associated with SARS-CoV-2 and influenza infections in a patient with central hypothyroidism after pituitary surgery.

Summary: We present the case of a 50-year-old Japanese woman who was transferred to our hospital with a 2-day history of fever, sore throat, and malaise. She was diagnosed with acromegaly 9 months ago while being treated for diabetic ketoacidosis, for which she underwent pituitary surgery. She was diagnosed with hypopituitarism postoperatively and was prescribed hydrocortisone and levothyroxine. Her glycemic control was good on metformin. Tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza were positive in the emergency room. Other laboratory findings included thyrotoxicosis (free T3: 9.13 pg/mL; free T4: 3.64 ng/dL; and thyroid-stimulating hormone (TSH): <0.01 μIU/mL) and a high C-reactive protein (CRP) level (3.84 mg/dL). The test for the TSH receptor antibody was negative. She had no apparent goiter and reported no tenderness in response to thyroid palpation. 99m-Technetium scintigraphy revealed decreased tracer uptake. Ultrasonography showed no hypoechoic lesions. Her thyrotoxicosis spontaneously resolved after 6 weeks. Although both anti-thyroglobulin antibody (TgAb) and anti-thyroid peroxidase antibody (TPOAb) were negative 9 months ago, TgAb was positive at admission. The test for TPOAb became positive 6 weeks later. These findings were suggestive of painless thyroiditis. In this patient, painless thyroiditis was believed to be caused by SARS-CoV-2 and influenza infections. Screening tests of thyroid function in patients with viral infections such as SARS-CoV-2 or influenza are recommended, even when thyroid gland pain or tenderness is not observed. Learning points: We describe a case of painless thyroiditis associated with SARS-CoV-2 and influenza infections. Although a few cases of painless thyroiditis associated with COVID-19 have been reported, no cases of painless thyroiditis associated with influenza have been reported. In this case, thyrotoxicosis developed immediately after the viral infection. In addition, tests for anti-thyroglobulin antibody and anti-thyroid peroxidase antibody were negative before the onset of symptoms. Tests for the former became positive at the time of onset of symptoms, whereas tests for the latter became positive several weeks after the onset of symptoms. Patients with viral infections such as SARS-CoV-2 and influenza, who had no goiter or thyroid tenderness, may develop painless thyroiditis; screening tests for thyroid function are recommended.