Painless thyroiditis incidentally diagnosed following SARS-CoV-2 infection.

A euthyroid woman in her 50s with papillary thyroid cancer and primary hyperparathyroidism was referred to our hospital for surgery. Her surgery was scheduled for 4 months later but was postponed because she was diagnosed with COVID-19. Five months after the first visit, she was admitted to our hospital to undergo the planned thyroid lobectomy and parathyroidectomy. Her blood tests on admission showed thyrotoxicosis, with negative thyroid-stimulating hormone receptor and thyroid-stimulating antibody. Notably, her anti-thyroglobulin antibody and anti-thyroid peroxidase antibody, which were originally negative, became positive after SARS-CoV-2 infection. She was diagnosed with painless thyroiditis. Her general condition and vital signs were stable, and the surgery was cautiously performed. Histopathological examination of the resected thyroid revealed papillary thyroid carcinoma, and the findings were consistent with painless thyroiditis. Her postoperative course was uneventful, and her thyroid function improved 2 weeks after the operation.