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Bone mineral metabolism and thyroid replacement therapy in congenital hypothyroid infants and young children
1Clinica Pediatrica III, Istituto Scientifico H San Raffaele, Università degli Studi di Milano, Italy.
Insights
Thyroid replacement therapy in congenital hypothyroidism (CH) does not affect bone mineralization in infants and children. A temporary increase in osteoblastic activity was noted in the initial months of treatment.
Area of Science:
- Pediatric Endocrinology
- Calcium Metabolism
- Bone Mineralization
Background:
- Hypothyroidism is linked to calcium metabolism issues and low bone density in adults.
- Congenital Hypothyroidism (CH) requires timely thyroid replacement therapy.
- The impact of this therapy on bone health in pediatric CH patients is not fully understood.
Purpose of the Study:
- To evaluate the effects of L-thyroxine therapy on calcium metabolism and bone mineralization in infants and children with congenital hypothyroidism.
- To assess biochemical markers of calcium metabolism and bone mineral content during thyroid replacement therapy.
Main Methods:
- A cohort of 116 Caucasian CH patients was studied across different age groups (diagnosis, 3, 6, 12, and 36 months).
- Measurements included serum calcium, phosphorus, magnesium, alkaline phosphatase (AP), parathyroid hormone (PTH), and osteocalcin (BGP).
- Bone mineral content (BMC) was measured at the radius; L-thyroxine dosage was adjusted over time.
Main Results:
- Elevated parathyroid hormone (PTH) and osteocalcin (BGP) levels were observed at 3 months, coinciding with peak L-thyroxine dosage.
- Mild, asymptomatic hypercalcemia occurred in 20 patients.
- Bone mineral content (BMC) and its annual increment were comparable to age-matched controls.
Conclusions:
- L-thyroxine replacement therapy does not negatively impact bone mineralization in CH infants and children.
- A transient increase in osteoblastic function is observed in the early stages of therapy.
- The study suggests that standard thyroid hormone replacement is safe for bone health in pediatric CH.
Abstract:
Impairment of calcium metabolism and low bone density have been found in hypothyroid adults. We investigated the effect of thyroid replacement therapy on calcium metabolism and bone mineralization in congenital hypothyroid (CH) infants and children. One hundred and 16 Caucasian CH consecutive patients were studied and were grouped according to their age: 23 patients at diagnosis, 20 at 3 mo, 24 at 6 mo, 25 at 12 mo and 24 at 36 mo. Thyroid replacement therapy was started at an initial dose of 6-8 micrograms/kg/day of L-thyroxine, and then decreased progressively. Calcium, phosphorus, magnesium, alkaline phosphatase (AP), parathyroid hormone (PTH) and osteocalcin (BGP) were measured as calcium metabolism indices. Bone mineral content (BMC) was measured at the mid-portion of the right radius AP, PTH and BGP concentrations were significantly higher in subjects at 3 mo of age (p < 0.05). This rise coincided with the end of the period of maximum dosage of L-thyroxine. Mild asymptomatic hypercalcemia was observed in 20 patients. All the other indices did not differ between age groups. BMC values and BMC annual increment were not different from those calculated for age-matched controls. We found that L-thyroxine replacement therapy does not alter bone mineralization of CH infants and children. Only a transitory increase of osteoblastic function was observed after the first few months of therapy.