Abstract #1406692: A Case of Anaplastic Thyroid Carcinoma and Hypocalcemia: Should We Be Monitoring for Hypocalcemia?

Abstract

Anaplastic thyroid carcinoma is one of the most aggressive and fatal forms of cancer. We present a patient with anaplastic thyroid carcinoma who developed hypocalcemia after diagnosis. A 77-year-old female with a history of hypertension and DM2 presented to the hospital for difficulty breathing and neck fullness for 2 weeks. Upon arrival, she developed stridor and was emergently intubated. Blood pressure was 155/75 mmHg, pulse was 80 beats per minute and respiratory rate 18 per minute on mechanical ventilation. A firm and diffusely enlarged thyroid was palpated on examination with difficulty discerning thyroid borders. CT scan revealed diffuse heterogenous enlargement of the thyroid measuring 43x40mm, a large mass of the right lobe with extracapsular extension, and invasion of surrounding structures. Initial admission labs showed TSH 0.010UIU/mL (0.35-5.5 UIU/mL), free T4 2.56 ng/dL (0.9-1.8 ng/dL), calcium 8.7mg/dL (8.6-10.4 mg/dL), magnesium 3.1mg/dL (1.8-2.5 mg/dL), phosphorus 4.9mg/dL (2.5-4.5 mg/dL), and creatinine 1.1mg/dL (0.50 - 1.20 mg/dL). She was started on high dose steroids for airway edema, which was continued for biochemical hyperthyroidism. A biopsy was positive for anaplastic thyroid carcinoma, and she was started on paclitaxel and carboplatin. On day 7, her corrected calcium dropped to 7.9mg/dL and ionized calcium was 3.72mg/dL (<4.60 or >5.10 mg/dL). PTH level was 61.68pg/mL (9-75 pg/mL) and 25OH vitamin D was 10.3ng/mL (25-80 ng/mL). She was given 1g of intravenous calcium gluconate and began daily calcium 500mg twice daily and cholecalciferol 5000IU daily. Genomic testing was positive for BRAF and targeted therapy with dabrafenib and trametinib was initiated. After 23 days of BRAF targeted therapy, a repeat CT showed radiographic improvement of the thyroid mass, measuring 33x20mm. Calcium levels improved to 9.8mg/dL. Repeat TSH was 0.086UIU/mL and free T4 was 0.730ng/dL and she was started on levothyroxine supplementation. She was transferred to a long-term care facility a few months later with plans for repeat blood work but ultimately passed away 3 months after initial diagnosis. The cause of hypocalcemia in this case is likely multifactorial. She was a critically ill patient with significant vitamin D deficiency, which can be contributing factors. However, the normal PTH level suggests that there may have been some degree of parathyroid dysfunction. Mechanisms that have been proposed for this are mass effect or tumor infiltration from thyroid cancer. Calcium levels should be checked upon diagnosis of anaplastic thyroid cancer and monitored closely throughout the clinical course.