Hyperthyroidism-Induced Hypercalcemia in a Young Male

Hyperthyroidism causes mild to moderate hypercalcemia in about 20% of patients but rarely causes severe hypercalcemia. Thyroid hormone stimulates bone turnover and elevates serum calcium, urinary and fecal calcium excretion. We present a case of a male with severe hypercalcemia due to thyroid storm.

Case Description : A 21-year-old male with T1DM, with multiple admissions due to DKA, presented to the ER with abdominal pain, nausea, vomiting, weight loss, headache, palpitations, and heat intolerance for the past 2 weeks. He was mildly agitated, had hypertension BP 180/110, HR 130, and temperature 99.1. Family history consisted of a maternal grandmother with Graves' disease. The CMP showed hypercalcemia with an albumin corrected calcium of 14mg/dl, hyperphosphatemia of 5.0, elevated AST 49, ALT 127, and normal ALP 126. TSH was undetectable < 0.01mlU/L, with elevated FT3 >20pg/ml and FT4 3.02ng/dl. Thyroid antibodies were elevated: TPO ab 1,055.7, TSI 4, and TRAB 10. The thyroid US showed an enlarged and hypervascular thyroid gland. The thyroid uptake scan was not done since he previously received contrast for a CT scan. Other causes of hypercalcemia were excluded. He did not have CKD, with normal creatinine before admission; hyperparathyroidism, with low PTH; malignancy, with normal PTHrP and normal CT of the abdomen and pelvis; multiple myeloma, with normal protein electrophoresis; hypervitaminosis D, with low Vitamin D level; granulomatous diseases, with normal CXR and low Vitamin D 1,25-OH. The patient was diagnosed with thyroid storm (Burch-Wartofsky score of 50), and hyperthyroid-induced hypercalcemia. He was started on NS 0.9% at 200ml/h, Vitamin D3 400IU QD, Methimazole 20mg BID, Propranolol 40mg BID, Cholestyramine 4gm BID, and SSKI 50mg QID. The surgeons recommended a thyroidectomy. After 5 days of treatment, the patient left AMA with resolved symptoms, normalization of FT3 3.0 and hepatic function, mild elevated FT4 1.64, significant improvement of corrected calcium 10.6, and creatinine 1.6. One month later, the patient showed up to his outpatient appointment with normal FT4 0.53, TT3 91.57ng/dl, and corrected calcium 9.4. He is scheduled for thyroidectomy in 1 week.

Discussion :

Our patient presented with non-PTH-mediated hypercalcemia. It is essential to consider hyperthyroidism in the differential diagnoses of hypercalcemia while ruling out other possible causes. We describe a unique case of severe hypercalcemia due to hyperthyroidism. The primary treatment is anti-thyroid medications and fluid rehydration. Hyperthyroidism-induced hypercalcemia is confirmed by the resolution of hypercalcemia with the control of thyrotoxicosis.