Metabolic bone disease

2021-03-05 12:00 AM

Also known as osteopenia of prematurity, the incidence is 32–90% in pre-term infants (mostly ELBW).

Metabolic bone disease

Also known as osteopenia of prematurity, the incidence is 32–90% in pre-term infants (mostly ELBW).

Cause

Chronic substrate deficiency—usually phosphate, rarely calcium or vita-min D. Risk is increased if:

  • prolonged PN;
  • breastfed (low in phosphate);
  • chronic diuretic treatment.

Presentation

  • Bone mineral biochemical derangement (see b Investigations); measure serum Ca2+, PO43-and alkaline phosphatase weekly in all infants under 33wks gestation.
  • ‘falls’ Linear growth.
  • Rib or distal long bone fractures.

Investigations

  • Biochemistry: PO43-<1.2mmol/L; Ca2+ >2.7mmol/L; alkaline phosphatase >1000IU/L.
  • Bone X-ray: osteoporosis, features of rickets, fractures.
  • Urine Ca2+/PO43-ratio >1 after 3wks of age (high renal PO43- reabsorption).

Treatment

  • Oral PO43-1mmol/kg/day supplement if milk fed.
  • Increase TPN Ca2+and PO43- (consult pharmacist).

Prevention

In infants <2kg or <33wks gestation:

  • Supplement breast milk with oral PO43-1mmol/kg/day (not required if fed preterm formula as already contains added PO43- );
  • Oral vitamin D 400IU/day;
  • Ensure TPN contains Ca2+2mmol/kg/day and PO43- 2.5mmol/kg/day (organic phosphate solution avoids mineral precipitation);
  • 10min/day of passive exercise appears beneficial.

Prognosis

Stature is reduced at age 18mths. Bone mineralization and fracture risk appear to be normal by 2yrs