SAT479 A Case of Thyroiditis Cause by Cabozantinib

Disclosure: S. Bulchandani: None. N. Janicic-Kahric: None. Introduction: Thyroiditis is an inflammatory disease of the thyroid; the cause can be autoimmune, infectious or drug induced. Patients can have an initial phase of hyperthyroidism (thyrotoxicosis) attributed to the release of preformed thyroid hormone from damaged thyroid cells. This can be followed by hypothyroidism, when the thyroid stores are depleted, and then eventual restoration of normal thyroid function. Some patients may develop permanent hypothyroidism.(1) We report a case of thyroiditis caused by cabozantinib. CASE REPORT: 39-year-old female presented with abdominal pain, vomiting and palpitations. Past medical history was significant for metastatic clear cell renal carcinoma. Eight weeks before the presentation, she had started on cabozantinib 60 mg daily as part of therapy for her renal carcinoma. On presentation, the patient’s temperature was 36.6 Celsius, heart rate was 118 beats/minute, blood pressure was 114/84 mm Hg and oxygen saturation was 100% on room air. Laboratory evaluation was notable for white blood cell count of 12.3 k/uL, Hemoglobin of 16.5g/dl, Platelet count of 573 k/uL bicarbonate level of 13 mmol/L, anion gap 24 mmol/L, Total bilirubin of 0.6 mg/dl, Aspartate aminotransferase of 36 units/L, Alanine aminotransferase of 30 units/L, Alkaline phosphatase of 121 units/L. Thyroid function tests revealed thyroid stimulating hormone (TSH) which was low at 0.045 uIU/ml and free thyroxine level (Free T4) which was elevated at 4.29 ng/dl. Thyroid function tests performed eight weeks prior to presentation showed TSH of 6.9 uIU/ml, attributed to immunotherapy that the patient received 1 month prior. She was admitted and received intravenous fluids. Prednisone at 40 mg orally daily was initiated. Labs demonstrated a decrease in Free T4 level. She was discharged on a tapering course of prednisone. Free T4 one week later was normal at 1.35ng/dl. Repeat laboratory evaluation three weeks later revealed that the patient had developed hypothyroidism with TSH level of 8.7 uIU/ml and she was started on 50 micrograms of levothyroxine. Cabozantinib was discontinued. Discussion: Tyrosine Kinase inhibitor therapy can result in clinically significant thyroid dysfunction. Cabozantinib treatment can result in thyroid dysfunction varying from subclinical hypothyroidism to symptomatic thyrotoxicosis. Early detection and close follow-up are essential to provide adequate management(2) Presentation Date: Saturday, June 17, 2023