Bilateral medullary nephrocalcinosis due to Vitamin D toxici
Vitamin D toxicity (VDT) is being increasingly reported from our country because of overzealous correction of VDD with mega-doses of vitamin D by the general healthcare providers. Nephrocalcinosis (NC) is a well-known but rare complication of VDT, which is usually irreversible.

Published in the in the Indian Journal of Endocrinology, the authors had previously reported an infant with acute VDT and NC. Briefly, the child presented to a local physician at the age of 8 months with symptoms of hypocalcemia and was prescribed one dose of intramuscular vitamin D containing cholecalciferol 600,000 units and oral calcium carbonate 500 mg daily.

However, the parents continued the intramuscular injection for 3 consecutive weeks, and a week following the final injection, the child was brought with features of hypercalcemia. The child was diagnosed to have parathyroid hormone (PTH)–independent hypercalcemia due to VDT (serum total calcium 11.5 mg/dL, 25-hydroxyvitamin D >100 ng/mL, and undetectable intact PTH) and was treated with intravenous normal saline and subcutaneous calcitonin injections, with improvement in hypercalcemic state.

During the initial presentation, he was also found to have hypercalciuria (24-h urine calcium >4 mg/kg and elevated urine calcium: creatinine ratio of 0.83) and bilateral medullary NC. In this report, we present the long-term follow-up data of this child.

The child was followed up annually with serum total calcium value, urine calcium: creatinine ratio, and ultrasonography of bilateral kidneys. On serial follow-up visits, serum calcium level, urine calcium: creatinine ratio, and estimated glomerular filtration rate (eGFR) remained normal, and there was no reduction in NC.

On a recent follow-up visit (14 years after the initial presentation), the child was growing normally with good scholastic performance. His total serum calcium value, urine calcium: creatinine ratio, and eGFR were normal at 9.4 mg/dL, 0.015, and 138 mL/min/1.73 m2, respectively. Ultrasonography and computerized tomography of kidneys revealed persistent medullary NC with minimal reduction in size.

Major takeaways:-
-The patient presented in infancy with VDT, hypercalciuria, and NC. NC persisted even after 14 years of the initial presentation despite correction in hypercalcemic and hypercalciuric state.

- However, in contrast to some of the existing literature, the child continues to maintain stable GFR. We hypothesize that deterioration of renal function is more likely in patients exposed to hypercalciuria for prolonged periods (such as PHPT, dRTA) or those with repeated, intermittent exposures (treatment with active vitamin D for hereditary hypophosphatemic rickets), compared with brief one-off exposure, as seen in this patient.

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