A case of adult-onset Still's disease (AOSD)-like manifestations abruptly developing during confirmation of a diagnosis of metastatic papillary thyroid carcinoma.

A 68-year-old Japanese man was admitted to our hospital suffering from abrupt onset of high fever accompanied by arthralgia, myalgia, sore throat, macular eruption, and liver dysfunction. Six months before the onset of these manifestations, (18)F-fluoro-deoxy-glucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) had detected, unexpectedly, three calcified thyroid lesions without (18)F-FDG uptake. Two months before the onset of the present manifestations, ultrasonography-guided fine-needle aspiration had led to a diagnosis of papillary thyroid carcinoma (PTC). Soon after the occurrence of the rheumatic manifestations, a subsequent (18)F-FDG PET/CT scan showed not only the three thyroid lesions, the same as those in the previous scan, but also (18)F-FDG uptake in the thyroid lesion. A diagnosis of adult-onset Still's disease (AOSD)-like manifestations associated with PTC was made, and treatment with 40 mg/day of prednisolone (PSL) resolved the symptoms promptly. PSL was gradually tapered, without recurrence of the (AOSD)-like manifestations. Five months after the initiation of treatment with PSL, total thyroidectomy, followed by (131)I thyroid ablation treatment, was performed while the patient was on a PSL dose of 18 mg/day. Seven months after the thyroidectomy, the dose of PSL was tapered to 2 mg/day, and neither the AOSD-like manifestations nor the PTC relapsed. On confirming a diagnosis of AOSD, it may be necessary to consider the presence of an associated malignancy, including solid tumors such as PTC.