SUN-390 - The Coaxial Needle and the Damage Done: A Unique Case of Traumatic Biopsy Induced Thyrotoxicosis in Metastatic Thyroid Cancer

Introduction:
Hyperthyroid state in relation to thyroid malignancy is extremely rare due to the majority of thyroid cancers being euthyroid. Metastasis to distant sites is rarer still, mostly with spread to local structures and lymph nodes. This case shows a patient who was found to have an iliac mass, that upon biopsy, was a metastatic follicular thyroid lesion. Her clinical course was complicated by a unique presentation of transient thyrotoxicosis due to release of preformed thyroid hormone following biopsy of the lesion.

Case:
An 83-year-old female with benign thyroid history, presented to the ED with atraumatic back pain with initial CT imaging showing a 14 cm mass eroding the left iliac and adjacent sacrum. Biopsy was performed and in the 5 days awaiting pathology results the patient developed palpitations, worsening tachycardia, and new onset atrial fibrillation. Pathology showed morphology and immunohistochemistry suggestive of thyroid carcinoma with cells akin to thyroid follicular cells and positive thyroglobulin staining.

Labs drawn 5 days after biopsy showed undetectable TSH and an elevated free T4, leading to initial suspicion of hyperactive thyroid malignancy. The patient was started on propylthiouracil and adjunct cholestyramine to control her hyperthyroid state with whole body RAIU deferred until the patient showed consistent improvement in thyrotoxic symptoms and with labs. With the initiation of suppressive thyroid medications, oncology assumed care starting with palliative radiation (with intention to start lenvatinib) and CARIS testing which returned with findings consistent with follicular thyroid cancer.

One month following admission and prior to initiation of lenvatinib, the patient became euthyroid on labs with eventual discontinuation of medications. Subsequent vitals were similarly stable with resolved atrial fibrillation. Whole body RAIU was performed showing a hypofunctional defect of the right thyroid lobe and radioiodine uptake in the left pelvis. The patient remained euthyroid on repeated labs and visits. Unfortunately, going forward the patient tolerated the lenvatinib for only one month due to painful mucosal ulcers. At the time of the composition of this abstract, the patient has opted for palliation.

Discussion:
Thyrotoxicosis in the setting of evaluation of thyroid malignancy is an exceptionally uncommon occurrence with metastases beyond local lymph nodes and structures being almost equally as rare. This case shows transient hyperthyroidism due to release of preformed thyroid hormone from biopsy of a metastatic lesion. Though unique, this highlights a relatively novel possible differential when it comes to symptoms of hyperthyroidism when evaluating thyroid malignancy. In terms of management there was high utility in frequent follow-up of thyroid function tests and symptomatic re-evaluation during the acute hyperthyroid prodrome.

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