A 77-year-old woman with no past history of interest consulted for a scalp lesion of more than two years' evolution with progressive growth over the last year, which bothered her when rubbed. It was a 6 mm hard erythematous-violaceous papular lesion in the parietooccipital region. This lesion was excised by slicing and silver nitrate, it bled a lot and it was not possible to obtain a sufficient sample for anatomopathological study (AP). After 6 months, the lesion grew again with similar characteristics in the same place, and was removed by elliptical excision and electric scalpel. The AP analysis reported the presence of differentiated thyroid tissue in the skin. The tumour was located in the middle and deep dermis and consisted of follicular structures of variable sizes containing colloid material with peripheral vascularisation and lined by a row of cubic cells with a low number of mitoses. Immunohistochemical examination detected intense cytoplasmic and intracolloid expression of thyroglobulin, keratin 7 and 19. With these findings the patient was referred to us for evaluation of metastasis of previously unknown thyroid cancer.

In the anamnesis the patient was asymptomatic and had no medical history of interest. Physical examination revealed a grade Ib goitre with a 2-3 cm nodule in the LTD that ascended well on swallowing, with no palpable lymph nodes, the rest being normal. Complementary tests: TSH 0.55 mU/L (0.35-5.5), T4l 1.23 ng/dL (0.8-1.76), T3l 3.19 ng/mL (2.3-4.2), undetectable anti-TPO and anti-TG antibodies and negative TSI, which have remained the same throughout follow-up. Thyroid ultrasound showed a multinodular goitre, with a dominant nodule measuring 25 x 15 mm of mixed echogenicity with hyper-hypoechoic areas and coarse calcifications in the LTD, and poorly defined hypoechogenic areas in the caudal area, where the FNA was performed and reported as a follicular tumour. One month later, a thyroidectomy plus lymphadenectomy of the central compartment was performed. The intraoperative biopsy was reported as papillary carcinoma. AP analysis of the surgical specimen was reported as mixed papillary and follicular carcinoma, well differentiated (90%) and solid with 10% poorly differentiated, partially encapsulated with extensive infiltration of the capsule and its vessels. The size of the encapsulated portion was 15 mm and 30 mm for the whole tumour. No extrathyroidal extension was seen and the surgical margins were free, the closest being 1 mm posterior. When the central compartment was emptied, 4 lymph nodes were obtained and found to be free of tumour.

An extension study was performed before radioiodine treatment by means of a metabolic study with 8.26 mCi of 18FDG, brain and pelvic MRI and bone scintigraphy, which was negative. Seventy days after the intervention, 104.7 mCi of I131 was administered after TSHrh. Baseline serum TG was 351 µg/L (1.6-60). Stimulated TG 1788.7 µg/L (47-10000) with baseline TSH of 117 mU/L (0.37-4.7). Post-I131 RCT showed post-thyroidectomy remnants located in the left posterior chamber, together with diffuse miliary involvement in both lung parenchyma compatible with metastasis. One month after radioiodine ablation and on treatment with 100 µg levothyroxine, he presented TG 37 µg/L (1.6-60), TSH 1.96 mU/L and T4l 1.43 ng/dL, at which time the dose of levothyroxine was increased to 125 µg. At the evaluation 6 months after radioiodine ablation the TG was 2.78 with TSH 0.03 and T4l 1.96, so she was given another dose of radioiodine of 125 mCi; and 2 months later TG<0.20 µg/L was detected with TSH 0.04 mU/L and T4 1.6 ng/dL. The patient will be re-evaluated in 4 months by quantification of stimulated TG after TSHrh and subsequent RCT to confirm cure.

