Distant, solitary skeletal muscle metastasis in recurrent papillary thyroid carcinoma.

BACKGROUND: Papillary thyroid cancer (PTC) is the most common differentiated thyroid carcinoma. Metastases usually occur in regional lymph nodes or to lungs. Distant metastases to skeletal muscle are rare. Here, we report a patient with a solitary metastasis to skeletal muscle.

PATIENT FINDINGS: A 31-year-old woman was found on routine physical examination to have a 1-cm nodule in the right thyroid lobe. The patient underwent endoscopic total thyroidectomy with central cervical lymph node dissection in April 2008. Pathological analysis showed a 1.5 × 0.9 cm PTC in the right thyroid lobe with extension into perithyroidal soft tissue and lymph node involvement (all six central lymph nodes examined were positive). After surgery, she received 100 mCi of radioactive iodine. Subsequently, the patient was found to have a lateral neck recurrence and, therefore, underwent right unilateral modified radical neck dissection followed by additional radioactive iodine ablation. In February 2010, her serum thyroglobulin was 19.4 ng/mL, but the neck ultrasound was negative. However, a fluorodeoxyglucose (FDG) positron emission tomography scan showed focal FDG uptake in the vastus medialis muscle of the right distal femur. A 0.9 × 0.5 cm, well-defined, whitish mass in the vastus medialis muscle was confirmed on histopathology to be metastatic PTC.

SUMMARY: Here, we report an adult woman who presented with a thyroid nodule that was noted to be PTC on histopathology after total thyroidectomy. Almost 2 years later, she was noted to have had focal FDG uptake consistent in the region of the right femur. A solitary metastasis of PTC in the right vastus medialis muscle was resected. A MEDLINE (Medical Literature Analysis and Retrieval System Online) search showed that this is only the third report of PTC with a distant, solitary skeletal muscle metastasis.

CONCLUSIONS: Distant skeletal metastasis in PTC is very rare. Until the availability of FDG to detect skeletal metastasis of PTC, they may have been more difficult to discern.