Paediatrics: Hypocalcaemia

Hypocalcaemia

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

• Prematurity
• Maternal diabetes
• Maternal pre-eclampsia
• RDS

Late neonatal causes

• Cow’s milk hyperphosphataemia
• Maternal hypercalcaemia
• Congenital hypoparathyroidism

Causes in infancy

• Nutritional rickets
• Pseudohypoparathyroidism type 1a

Childhood causes

• Pseudohypoparathyroidism type 1b
• Hypoparathyroidism

Iatrogenic causes

• Chemotherapy agents, e.g. cisplatin
• Anticonvulsant agents, e.g. phenytoin

Investigations

• 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.

Treatment

Acute treatment

Chronic treatment

• 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.

Hypoparathyroidism

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);
• radiotherapy.
• Failure in PTH secretion: magnesium deficiency.
•  Failure in PTH action: pseudohypoparathyroidism.

Investigations

• Plasma calcium: low.
• Plasma phosphate: high.
• Serum PTH: low.

Pseudohypoparathyroidism (PHP)

Characterized by end-organ resistance to the actions of PTH. It is a genetic disorder due to a defect in the G_s 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.