Hypocalcaemia

Pathophysiology:

Hypocalcaemia may be due to:

• Deficiencies of calcium homeostatic mechanisms
• Secondary to high phosphate levels

Causes of hypocalcaemia:

Increased phosphate levels:

• Chronic renal failure (common)
• Phosphate therapy

Hypoparathyroidism:

• Post-surgical
• DiGeorge syndrome (congenital condition where the hypoparathyroidism is associated with intellectual impairment, cataracts and calcified basal ganglia)
• Idiopathic hypoparathyroidism (rare)
• Severe hypomagnesaemia

Vitamin D deficiency:

• Osteomalacia
• Vitamin D resistance

Resistance to PTH:

• Pseudohypoparathyroidism

Drugs:

• Calcitonin
• Bisphosphonates

Miscellaneous:

• Acute pancreatitis (quite common)
• Citrated blood in massive transfusion

Symptoms of hypocalcaemia:

At first there is:

• Paraesthesiae
• Circumoral numbness
• Cramps
• Anxiety
• Tetany

Followed by:

• Convulsions
• Laryngeal stridor
• Dystonia
• Psychosis

Signs of hypocalcaemia:

Chvostek’s sign:

• Gentle tapping over the facial nerves causes twitching of the facial muscles

Trousseau’s sign:

• Inflation of the sphygmomanometer cuff above systolic pressure for 3 minutes induces titanic spasm of the fingers and wrist

Investigations:

• Serum calcium
• Serum and urine creatinine (for renal disease)
• PTH levels (absent or inappropriately low)
• Parathyroid antibodies (present in idiopathic hypoparathyroidism)
• Serum 25-hydroxy vitamin D level (low in vitamin D deficiency)
• X-rays of the metacarpals:
• Showing short fourth metacarpals in pseudohypoparathyroidism

Treatment:

Urgency of treatment depends on the severity of the symptoms and the degree of hypocalcaemia.

If severe with Tetany:

• IV calcium is given (10mL initially, then 10-40mL of 10% calcium gluconate in 1L of 0.9% saline over 4-8 hours