LAUSR

Dear Sir, Papillary thyroid microcarcinoma is commonly considered to have a good prognosis. We report the case of a 47year-old male patient, who was referred to our Institution for a papillary thyroid microcarcinoma infiltrating perithyroidal fibroadipose tissue, treated in 2006 with surgery and in 2007 with I-therapy (3700 MBq). He was followed up between 2007 and 2017 and was free of disease based on serum Tg and ultrasonography; then, suddenly, some pimple-like neck skin lesions appeared that were not responsive to topical therapy. The patient underwent excision of these skin lesions, which at histopathology were found to originate from papillary thyroid carcinoma. A subsequent neck ultrasonography revealed a 9 × 4-mm nodule in the sternothyroid muscle and a 4-mm nodule in the sternocleidomastoid muscle (Fig. 1). Diagnostic I whole-body scan performed after recombinant human TSH (rhTSH) stimulation was negative (Fig. 2a, b), but serum Tg was detectable (16/02/2018:TSH > 100 mIU/L; Tg 2.1 μg/L; ioduria 2 μg/dL; anti-Tg antibodies were negative). Concomitant F-fluorodeoxyglucose positron emission tomography/ computed tomography (F-FDG PET/CT), performed in spite of low values of stimulated serum Tg [1–3], showed radiopharmaceutical accumulation in the nodules revealed by echography (Fig. 2c–e), suspicious for malignancy. Fine-needle aspiration cytology (FNAC) and Tg measurement in fine-needle washout fluids confirmed the suspicion. In the meantime, two new pimple-like neck skin lesions appeared (Fig. 2f). The patient underwent radioguided surgery after intranodular injection of 30 MBq of Tc-MAA (to localize the nodules in the muscle tissues). Pathological examination confirmed the presence of cutaneous and muscle lesions from papillary thyroid carcinoma (Fig. 2g, h). Differentiated thyroid cancers (DTC) are usually limited to the thyroid, even though some of them have aggressive behavior [4, 5]. Locoregional metastases can occur in the thyroidectomy bed or in neck lymph nodes; major sites of distant metastases of DTC are lung and bone, whereas minor sites include the brain, liver, skin, pleura, and muscle [6, 7]. Skeletal muscle metastases are extremely rare [6]. Yazici et al. reported a woman with right occipital bone metastasis from papillary thyroid microcarcinoma who, at post-therapy whole-body scan, also presented left lung and