MON-407 - Late Skeletal Metastases and Mechanical Spine Instability in Metastatic Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) is usually associated with excellent long-term outcomes. However, late metastatic disease can occur and presents unique management challenges. Skeletal metastases are uncommon and may be difficult to interpret when imaging findings and symptoms are influenced by mechanical spine disease rather than active tumor progression.

We present a 67-year-old woman with metastatic PTC initially treated with total thyroidectomy and radioactive iodine in 2006 for multifocal disease with follicular variant and insular features and mediastinal lymph node involvement. After a prolonged period of surveillance, she developed pulmonary metastases requiring surgical resection in 2019 and again in 2021. Rising thyroglobulin levels in 2023–2024 prompted further evaluation. FDG PET/CT demonstrated FDG-avid lytic lesions in the left fifth rib and L5 vertebral body, consistent with osseous metastatic disease. She completed palliative radiation therapy to both sites in April 2024.

Follow-up imaging through December 2025 showed stability of the rib lesion and no interval tumor progression at L5. However, there was progression of a pathologic L5 compression fracture with associated spinal canal and foraminal stenosis. Clinically, the patient reported mild, intermittent low back pain with occasional radicular symptoms. Her pain was manageable with intermittent NSAID use, bracing, physical therapy, and weight loss. She remained neurologically intact and declined surgical intervention.

This case highlights the importance of considering laboratory results, imaging findings, and clinical symptoms together when evaluating spinal lesions in metastatic thyroid cancer.

Conclusion:
Late skeletal metastases in papillary thyroid carcinoma may coexist with degenerative and mechanical spine pathology. Careful distinction between oncologic progression and structural instability can help avoid unnecessary escalation of therapy. In patients with stable disease and mild symptoms, conservative multidisciplinary management may be appropriate and effective.

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