Synchronous muscle and bone metastases in thyroid cancer

Simultaneous skeletal muscle and bone metastases in thyroid carcinoma are exceedingly uncommon. The objective of this report is to describe diagnostic and management challenges of thyroid cancer presenting with distant metastases over a decade after initial lobectomy. A 47-year-old man presented with a history of left thyroid lobectomy for a presumably benign nodule (pathology unavailable). Twelve years later he was found to have a 1.9 cm left thyroid nodule with calcifications. Fine-needle aspiration revealed atypical cells of undetermined significance, and subsequent left hemithyroidectomy revealed benign hyperplastic nodule. Follow-up imaging identified new right thyroid nodules that progressively enlarged over three years but were cytologically benign on repeated fine needle aspirations. He then presented with left deltoid muscle mass, which was excised, and pathology revealed nodular thyroid tissue with mild atypia. A whole-body radioactive iodine I-131 scan demonstrated uptake in thyroid bed, left iliac crest, and sacrum. Right thyroid lobectomy showed 0.17 cm follicular variant of papillary thyroid carcinoma with BRAF V600E mutation. Levothyroxine was started, and I-131 radioiodine therapy (98.3 mCi) was performed; however, repeat 131 whole-body scan revealed residual focus within right midline thorax. Although papillary thyroid microcarcinoma was identified, the metastatic pattern could be consistent with a missed well-differentiated follicular thyroid carcinoma at initial surgery. This case highlights the importance of long-term surveillance and continuity of care in thyroid cancer. Initial or recurrent thyroid cancer recurrence may present with uncommon patterns of metastases. • Very rare mPTC cases have potential of aggressive course with distant metastases. • Muscle metastasis is rare and unusual as the initial presentation of thyroid cancer. • Distant metastases without locoregional spread are rare but warrant close monitoring.