Orbital metastasis from medullary thyroid carcinoma.

A 46-year-old woman with known multiple endocrine neoplasia type 2A was referred for evaluation of left-sided progressive diplopia and proptosis. She was given the presumptive diagnosis of progressive thyroid-associated orbitopathy. Clinical examination revealed significant proptosis and restricted motility of the left eye. Serial CT demonstrated a marked progression in size of the left inferior rectus muscle. This was postulated to be a rare case of metastasis of a medullary thyroid carcinoma to the left inferior rectus muscle, which was confirmed by lateral orbitotomy and excisional biopsy. The presence of unilateral proptosis raises the possibility of intraorbital or intracranial disease and warrants further investigation. Detection of metastases and subsequent surgical excision or debulking has palliative benefits, including prevention of compression or invasion of major structures and cooperative planning with oncology and participation in treatment regimens that may prove beneficial in patients with metastatic medullary thyroid carcinoma.