Endocrine Abstracts

Introduction: Severe hypercalcemia is defined as a total serum calcium level >14 mg/dl or ionized calcium >10 mg/dl . The most common causes are primary hyperparathyroidism (PHPT) and neoplasms (90% of cases). Vitamin D intoxication is an extremely rare cause.

Case Report: A 56-year-old man presented to the emergency department with vomiting, generalized weakness and complaints of imbalance over one week. Upon physical examination, he displayed confusion, trunk and limb ataxia and abolished osteotendinous reflexes. He had history of multiple endocrine neoplasia (MEN) 1 and PHPT with a hypercaptant left inferior parathyroid on scintigraphy. Six weeks before admission, he underwent parathyroidectomy of the inferior glands (histology: hyperplasia). Postoperatively, calcium and parathyroid hormone (PTH) declined, reaching levels of 6.0 mg/dl for calcium and 0.3 pg/ml for PTH. His 25(OH)vitamin D level was 22 ng/ml. Supplementation was adjusted, and he was discharged with a regimen of Calcium Carbonate + Colecalciferol 1500 mg + 400IU, 2 tablets every 8 hours, and Calcitriol 0.25µg, 1 tablet every 6 hours. Upon admission, the patient’s total serum calcium was exceptionally elevated at 23.8 mg/dl, with albumin measuring 4.4 g/dl, creatinine at 4.35 mg/dl (baseline 1.62), PTH <0.5 pg/ml, and 25(OH)vitamin D at 42 ng/ml. Phosphate and magnesium levels were within normal ranges. The therapeutic approach encompassed intensive fluid therapy, furosemide administration, calcitonin and zoledronic acid. Subsequently, the patient’s serum calcium exhibited a gradual reduction, reaching 7.9 mg/dl by the 10th day of hospitalization. At this time, the patient reported that he had been taking not one but four calcitriol tablets every 6 hours due to a misunderstanding of the prescription, supporting the hypothesis of 1,25(OH)vitamin D intoxication. Oral supplementation was re-initiated. Serum calcium continued to decrease, reaching 6.6 mg/dl on the 13th day of hospitalization, which required intravenous calcium and adjustments to oral supplementation. Upon discharge, there was an improvement in renal function (creatinine 2.06 mg/dl), and serum calcium was stabilized at 8.4 mg/dl with a regimen of Calcium Carbonate + Colecalciferol 1500 mg + 400IU 2+2+1+2 tablets and Alfacalcidol 1 mg 1+1 tablet.

Conclusion: The possibility of vitamin D intoxication should be considered in the presence of hypercalcemia, decreased PTH, and no suspicion of malignancy. The patient was taking 4 mg of calcitriol daily, a dose much higher than recommended for hypoparathyroidism treatment (0.5–1.0 μg/day). This case reminds us of the need to regularly monitor calcium levels in patients with post-surgical hypoparathyroidism and ensure that patients understand the proposed therapeutic regimen.