Immunoglobulin G4-related thyroiditis (IgG4-RT) is associated with chronic autoimmune thyroid diseases such as Hashimoto’s thyroiditis, Graves disease and Riedel’s thyroiditis. Although thyroid papillary carcinoma developed in the background of IgG4-RT has been reported, there is no report on IgG4-RT established from preexisting papillary thyroid cancer. Herein, we report a case of IgG4-RT documented by surgery during the active surveillance (AS) for papillary thyroid microcarcinoma (PTMC).
A 60-year-old male underwent third annual thyroid ultrasonography (US) for follow-up of a 2x2x2 mm-sized PTMC in the lower portion of the left thyroid lobe. The PTMC was cytologically confirmed 3 years ago by fine-needle aspiration (FNA) and the patient opted for AS rather than lobectomy. On US, the tumor was significantly increased to 2x5x6 mm (figure 1) and abutted the trachea and posterior thyroid capsule. Lobectomy was performed, and histology confirmed IgG4-RT without any foci of PTMC. Abdominopelvic CT showed no other organ involvement. The patient has been well without levothyroxine replacement after the surgery.
As AS is increasingly accepted for a therapeutic option in PTMC, our case raises an important clinical question. Whether the additional FNA is needed before the decision for surgery when the tumor on AS has been grown. Clinicians should be aware of that IgG4-RT may be focal and can be developed from the preexisting PTMC possibly due to anti-tumor immunity.