7027 A Rare And Multifactorial Etiology Of Severe Parathyroid Hormone Independent Hypercalcemia In An Adult Female With Rett Syndrome

Abstract Disclosure: M.I. Foo: None. M. Thompson: None. Background: Symptomatic hypercalcemia is a rare, but potentially life-threatening disorder. Although dehydration is an unusual cause of severe hypercalcemia, in the appropriate clinical setting dehydration may amplify underlying mild or moderate hypercalcemia to dangerous levels.Case: A 46-year-old non-verbal, non-mobile Caucasian female with Rett Syndrome (RS) with Stage III Chronic Kidney Disease (CKD3) who is dependent on percutaneous endoscopic gastrostomy (PEG) tube for nutrition and known PTH independent hypercalcemia of unknown etiology presented to the hospital with intractable vomiting and constipation, an outpatient serum calcium level of 16.0 mg/dL, and serum creatinine 4.03 mg/dL (baseline 1.2 mg/dL). Initial laboratory assessment revealed elevated corrected serum calcium levels (15.7 mg/dL), with appropriately suppressed PTH levels (12.5 pg/mL) and hypernatremia (146 mmol/L). Thyroid function tests, both Vitamin D 1,25(OH)2D and D 25(OH)D levels and PTH-RP were normal. Computed tomography of the abdomen and pelvis revealed bilateral nephrolithiasis and moderate stool burden, but no evidence of malignancy or granulomatous disease. Skeletal scintigraphy was also without evidence of osseous metastatic disease or Paget’s disease of bone. An in-depth interview with the patient’s caregiver uncovered that the patient had a relative intolerance to enteral hydration and had been receiving minimal water flushes prior to admission, contributing to severe dehydration. Hypercalcemia was ultimately ascribed to prolonged immobilization due to RS compounded by inadequate fluid intake and auto-diuresis secondary to hypercalciuria in the setting of CKD (prior baseline eGFR 45 mL/min/1.73m2).Outcome: The patient's hypercalcemia improved after a multidisciplinary and multi-directed approach involving intravenous and enteral fluid resuscitation, calcitonin, furosemide, and ultimately zoledronic acid following improvement in creatinine with fluid resuscitation. The dietary service employed a strategy of 24-hour enteral feeding, increasing both the frequency and amount of enteral water, which the patient tolerated well, and provided her with a new pump for home use. Education on monitoring tube feed tolerance and providing adequate enteral hydration was provided to both the caregiver and group home. On discharge, eGFR stabilized at 33 mL/min/1.73m2 and corrected calcium stabilized at 10.0–10.4 mg/dl. She was provided with an endocrinology follow-up to continue bisphosphonate therapy.Discussion: Hypercalcemia of immobility should remain a differential diagnosis in severe hypercalcemia, especially PEG tube dependent patients with underlying kidney disease. This case highlights the importance of thorough history taking and a multidisciplinary strategy to guarantee optimal care and mitigate potential adverse outcomes in medically complex patients. Presentation: 6/2/2024