Most causes of low calcium (hypocalcaemia) can be explained by abnormalities of vitamin D or PTH metabolism or by disordered kidney function.
Most causes of low calcium (hypocalcaemia) can be explained by abnormalities of vitamin D or PTH metabolism or by disordered kidney function. The principal manifestations of hypocalcaemia are related to neuromuscular irritability and include tetany and paraesthesiae.
- Hypocalcaemic seizures (grand-mal type) or laryngeal spasm may occur acutely.
- Cardiac conduction abnormalities (prolonged QT interval, QRS and ST changes, and ventricular arrhythmias) may be seen.
Chronic hypocalcaemia may be asymptomatic. The child’s age is helpful in determining the differential diagnosis of hypocalcaemia.
Causes of hypocalcaemia
Early neonatal causes
- Maternal diabetes
- Maternal pre-eclampsia
Late neonatal causes
- Cow’s milk hyperphosphataemia
- Maternal hypercalcaemia
- Congenital hypoparathyroidism
Causes in infancy
- Nutritional rickets
- Pseudohypoparathyroidism type 1a
- Pseudohypoparathyroidism type 1b
- Chemotherapy agents, e.g. cisplatin
- Anticonvulsant agents, e.g. phenytoin
- Plasma calcium.
- Plasma phosphate.
- Serum PTH. Note: Low or even normal PTH concentration implies a failure of PTH secretion.
- Plasma vitamin D.
- Plasma magnesium.
- X-ray of the skull. Chronic hypocalcaemia: basal ganglia calcification may be seen.
- Should be directed at the underlying cause.
- Oral calcium supplements, together with oral vitamin D therapy in the form of calcitriol (1-A calcidiol) are often required to maintain plasma calcium levels within the normal range.
Low serum parathyroid hormone levels in childhood may be due to the following:
- Failure in parathyroid development (agenesis/dysgenesis):
- isolated defect: X-linked recessive;
- associated with other abnormalities, e.g. DiGeorge syndrome, Kearnes–Sayre syndrome.
- Destruction of parathyroid glands:
- autoimmune—type 1 autoimmune polyendocrinopathy;
- surgery (post-thyroidectomy);
- Failure in PTH secretion: magnesium deficiency.
- Failure in PTH action: pseudohypoparathyroidism.
- Plasma calcium: low.
- Plasma phosphate: high.
- Serum PTH: low.
Characterized by end-organ resistance to the actions of PTH. It is a genetic disorder due to a defect in the Gs A-adenylate cyclase signalling system common to the PTH receptor and other endocrine receptors belonging to the G protein-receptor family (e.g. TSH, LH, FSH). See Table 12.2.