SUN-096 Incidentally Found Severe Hypercalcemia in a Pediatric Patient, Diagnostic Challenge

Introduction: Idiopathic infantile hypercalcemia is an intriguing feature of Williams syndrome (WS), occurring in ~15% of diagnoses and is typically not clinically severe. Symptomatic hypercalcemia usually resolves during childhood, but lifelong abnormalities of calcium(Ca) and vitamin D metabolism may persist. The cause of the abnormality in Ca metabolism is still unknown. Hypercalciuria generally accompanies hypercalcemia, but isolated hypercalciuria, especially after infancy, can also occur. Nephrocalcinosis is relatively rare, found in less than 10% of patients undergoing renal ultrasonography. We report a 13-month-old female infant with a history of peripheral pulmonary stenosis and constipation, who presented with severe hypercalcemia that led to a new diagnosis of WS. Case presentation: A 13-month-old girl with a history of peripheral pulmonary stenosis, global developmental delay, and constipation presented to the neurology clinic for evaluation of gross motor delay. She was found to have upper body part hypotonia, decreased reflexes, and on laboratory evaluation, severe hypercalcemia with Ca level of 15.0 mg/dL (8.7 - 10.7). The patient was admitted for management of severe hypercalcemia. Physical exam was also remarkable for subtle features of WS: a happy baby, very social, with prominent eyes, full cheeks, flat nasal bridge, round nasal tip, full lips, and a wide smile. Repeated Ca level on admission was 15.9 mg/dL, with normal albumin level of 4.6 g/dL (2.9-5.5), elevated ionized calcium (iCal) of 1.99 mmol/L (0.95 - 1.32), and intact parathyroid hormone (PTH) of <4.0 pg/mL (8.0 - 85.0). Further evaluation revealed a normal 25 hydroxy-vitamin D:41 ng/mL (30-80) and low 1,25-dihydroxy vitamin D:10pg/mL (31-87). Further evaluation revealed elevated urine calcium to creatinine ratio of 0.7 (normal for age <0.56) and renal ultrasound remarkable for medullary nephrocalcinosis. The patient had a complete blood count within normal limits and a PTH related protein of 26 pg/mL (14-27), ruling out malignancy. Hypercalcemia responded well to intravenous fluids and diuretics, the patient being discharged home after two days on furosemide and potassium supplements with close electrolytes monitoring. The patient required calcium reducing therapy for four months to maintain Ca levels within 9-12 range. The medication was decreased gradually based on calcium and ical levels. The patient is currently doing well, with a normal calcium level, and has being off medication for the past three months. Conclusion: This is a rare case of severe hypercalcemia, which led to the diagnosis of WS. Although idiopathic infantile hypercalcemia occurs in 15% of patients with WS, usually the presentation is mild, and the patients do not require medical interventions. Our patient presented with severe hypercalcemia and subtle physical features of WS that led to genetic testing and final diagnosis.