Graves’ Disease Induced Severe Hypercalcemia

Introduction: Hyperthyroidism is a well-known non-parathyroid hormone-mediated cause of hypercalcemia. Hypercalcemia associated with thyrotoxicosis is usually asymptomatic. Increased osteoclastogenesis is one of the mechanisms underlying this etiology. Hyperthyroidism is associated with mild to moderate levels of hypercalcemia in approximately 20% of patients, but severe hypercalcemia is rare. We report a case of a male with Grave’s disease-induced symptomatic severe hypercalcemia. Clinical Case: A 36-year-old male with type 2 diabetes mellitus and arterial hypertension who was transferred from another institution to our Emergency Department due to suspected primary hyperparathyroidism for Endocrinology Services evaluation. Family history is non-contributory. Patient reports palpitations, irritability, and unintentional weight loss of approximately fifty pounds in nine months. One month ago, he started with constipation, anxiety, depression, abdominal discomfort, nausea, and vomiting for which decided to seek medical attention. Physical examination was remarkable for tachycardia, dry mucous membranes, and goiter. Laboratory tests showed lipase 69 U/L (13-60U/L), albumin-corrected calcium 14.3 mg/dL (8.8-10.3mg/dL), phosphorus 3.30 mg/dL (2.4-4.2mg/dL), magnesium 1.58 mg/dL (1.8-2.2mg/dL), creatinine 1.38 mg/dL (0.90-1.30 mg/dL), alkaline phosphatase 77 IU/L (43-115IU/L), iPTH 4 pg/mL (11-67pg/mL), PTHrp <0.4 pmol/L (≤4.2pmol/L), 25-OH vitamin D 32.1 ng/mL (30-100ng/mL), 1,25-dihydroxyvitamin D <5.0 pg/mL(19.9-79.3pg/mL), hemoglobin 11.6 g/dL (14-18g/dL), negative serum and urine protein electrophoresis, TSH 0.003 uIU/mL (0.45-5.33 uIU/mL), free T4 2.80 ng/dL (0.71-1.85ng/dL), total T3 2.57 ng/mL (0.80-2.00ng/mL), TSI: 486% (<140%), urine calcium 24hr 525mg/day (100-300mg/day). Thoracic and abdominopelvic CT scan without contrast was unremarkable for masses, adenopathies, osseous lesions, or acute abdominal processes. Patient was treated with IV isotonic saline and methimazole 10mg oral daily with resolution of symptoms. Finally, diagnosed with Graves’ disease as the cause of hypercalcemia after ruling out other etiologies. He was discharged home with calcium levels 10.8 mg/dL, normal renal function, methimazole, and follow up with Endocrinology Services. Conclusion: This is a case of an atypical presentation of hyperthyroidism-induced symptomatic hypercalcemia. It is important to consider hyperthyroidism in the differential diagnoses of severe hypercalcemia. Prompt suspicion is essential due to the effective treatments available for Graves’ disease. Early treatment of hypercalcemia is important for quick resolution of symptoms and decreased associated mortality.