Are we undertreating calcium deficiency in metabolic bone disease of prematurity? A case report and review

BACKGROUND: Both calcium (Ca) and phosphorus (P) are needed to prevent and treat metabolic bone disease (MBDP). However, the predominant focus of many treating neonatologists lies in supplementing P and vitamin D. In this report, we describe a VLBW infant with severe MBDP due to inadequately treated calcium deficiency and discuss the need to recognize this entity. CASE DETAILS AND MANAGEMENT: A 25-week, 700 gm baby boy had chronic lung disease and necrotizing enterocolitis. He received total parenteral nutrition, budesonide, furosemide, and caffeine. With high serum alkaline phosphatase (ALP: 1,700 IU/L) and low P (2.8 mg/dl), MBDP was diagnosed at 12 weeks, started on oral phosphate, human milk fortifier, and 1,400 IU/d of vitamin D before discharge. He was readmitted 2 weeks later with decreased lower limb mobility and respiratory distress. X-rays revealed severe osteopenia and fractures of both femurs. Serum P was 4.6 mg/dl but ALP was high (1,700 IU/L), and Ca was low (6.4 mg/dl). Parathyroid hormone (PTH: 605 pg/ml) and 25-hydroxy Vitamin D (25 OHD > 200 ng/ml) were very high. We discontinued his P and vitamin D, hypocalcemia treated with IV Ca gluconate, later oral Ca citrate, and calcitriol. Phosphate was added after normalization of Ca. Over the next many weeks, X-rays and biochemistry improved. DISCUSSION: MBDP results from both Ca and P deficiencies, especially in VLBW infants with comorbidities. P supplementation without treating underlying calcipenia can precipitate hypocalcemia and worsen osteopenia with disastrous consequences. In severe calcipenia, active vitamin D might have a role in addition to an appropriate dose of elemental calcium.