Occult Papillary Carcinoma Thyroid with Solitary Appendicular Bone Metastasis in Proximal Humerus - A Case Report.

Introduction: An occult presentation of primary thyroid malignancy refers to a clinically silent primary tumor that initially manifests through metastasis or secondary paraneoplastic phenomena. Papillary carcinoma is a well-recognized thyroid malignancy associated with this pattern of presentation, but bone metastases are uncommon in occult papillary thyroid carcinoma (OPTC), with reported cases typically involving the axial skeleton.

Case report: A woman in her 70s presented with swelling and pain in her right arm. Examination revealed an oval swelling on the proximal humerus. Radiographs and magnetic resonance images suggested a lytic lesion in the proximal humerus. Upon metastatic workup, biopsy, and immunohistochemistry, the diagnosis turned out to be metastasis from occult papillary thyroid cancer.

Conclusion: Bone metastases are uncommon in OPTC, with reported cases typically involving the axial skeleton. Metastasis to the appendicular skeleton as the initial presentation is exceptionally rare.