(6.15) A Case of Metastatic Papillary Thyroid Carcinoma in the Lumbar Spine without Evidence of Primary Cancer in the Thyroid

We report a case of metastatic follicular variant of papillary thyroid carcinoma to the lumbar spine, without histopathologic evidence of primary cancer originating from the thyroid.

Case(s) Description :

A 35-year-old female experienced six weeks of atraumatic back pain accompanied by bilateral lower extremity neuropathy, prompting her to undergo an MRI. The scan revealed a mass causing a pathologic fracture at L5 with significant lateral recess encroachment. Neurosurgery performed the operation on the spine. Unexpectedly, the biopsy of the L5 vertebral body reported a follicular variant of papillary thyroid carcinoma, with no evidence of poor differentiation or anaplasia. Five years earlier, she had a left hemithyroidectomy due to dysphagia caused by a Bethesda category III 3.8cm x 2.8cm x 3cm left mid-thyroid nodule, which pathology indicated as a follicular adenoma. During this interval, she also underwent a total hysterectomy, bilateral salpingectomy, and left oophorectomy due to cervical dysplasia, dysmenorrhea, and pelvic pain. Pathology reported a focal high-grade squamous intraepithelial lesion without significant findings in both fallopian tubes and the ovary. Following the spinal procedure, she underwent a right thyroid lobectomy with right central compartment neck dissection. Pathology reported thyroid tissue and scattered lymphoid tissues at level 6, with no diagnostic abnormalities. Post-operative stimulated thyroglobulin was elevated at 2846 ng/ml (< 55) with negative anti-thyroglobulin antibody < 15 U/ml (0-60). A whole-body CT scan with IV contrast revealed no evidence of other distant metastasis. Additionally, a 131-iodine whole-body scan indicated she likely had non–iodine-avid disease. The patient was scheduled for the initiation of stereotactic body radiation therapy targeting the lumbar spine while awaiting further testing with a PET scan and pelvic ultrasound. The BRAF immunohistochemistry result is currently pending.

Discussion :

This case highlights the rare phenomenon of occult thyroid carcinoma. While lacking a known mechanism, metastatic thyroid cancer can manifest without an identifiable source from the thyroid. Studies have shown that poorly differentiated thyroid cancer with a BRAF mutation tends to be associated with lymph node metastasis, while those with an RAS mutation are more likely to show distant metastasis. Due to a significant elevation in thyroglobulin levels, the patient continues to require ongoing evaluation with further imaging and laboratory results. Unfortunately, the clinical outcome for the patient has become guarded due to metastatic disease that is not amenable to radioactive iodine therapy. According to the National Comprehensive Cancer Network guidelines, a tyrosine kinase inhibitor could be a potential subsequent therapy of choice. However, the toxicity of treatment and its impact on the quality of life must be carefully considered. Therefore, a multidisciplinary team effort is essential to improve the outcomes for the patient.