0835 Risks and consequences of nephrocalcinosis in premature infants

Nephrocalcinosis (NC) was first described in preterm infants some 25 years ago as a consequence of furosemide treatment that was popular at that time, directed towards the reduction of lung water in preterm neonates with chronic lung disease/bronchopulmonary dysplasia. However, while furosemide is no longer in vogue, NC continues to be an issue. The condition is defined simply as mineral precipitates in the renal parenchyma, but there may also be calcification/crystallization in the tubules, and occasionally stones are an associated feature. The deposits are mainly calcium oxalate but calcium phosphate deposits are also possible. The medulla is the primary site, probably due to the premature infant having relatively well-developed deep nephrons, long loops of Henle and low urine velocity, all of which, together with stone-promoting factors and reduced stone-inhibiting factors, place the infant at risk for NC. Ultrasound is the superior radiological investigation and is more accurate than CT and conventional x-rays. Early studies identified NC in up to two-thirds of ex-premature infants; however more recent evidence is that 7-41% of preterm infants of <32 weeks and <1500g may be affected. The immature kidney per se is the key factor, with the risk specifically increased as a result of hypercalciuria in premature infants (high urinary calcium/creatinine ratio), glucocorticoid administration (high calcium excretion), methylxanthine exposure for apnoea (hypercalciuric effect), acidosis (increased urinary calcium, decreased urinary pH), high calcium intake (to prevent rickets of prematurity), high phosphate intake in accordance with recommended daily allowance, and parenteral nutrition. Nephrocalcinosis will resolve spontaneously in the vast majority of infants (85% in the first years of life), but a small percentage will not be as fortunate and there may be consequences, mainly along the lines of mild chronic renal insufficiency, impairment of distal tubular function, and hypercalciuria. From the data it would appear that screening (specifically ultrasound) would be appropriate, with good follow-up required in up to 40% of at-risk neonates.

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Pediatr Nephrol 2008; DOI.1007/s00467-008-0908-9
Br J Radiol 2000; 73: 1185-91
Pediatr Nephrol 2004; 19: 616-20