Diagnosis

• exclusion of other causes of hypercalcaemia

• serum parathyroid hormone (elevated)

Hypercalcaemia

Suspect hypercalcaemia if there is weakness, tiredness, malaise, anorexia, nausea or vomiting, constipation, thirst, polyuria, drowsiness, dizziness, muscle aches and pains, visual disturbances. Measure urea and electrolytes (especially calcium), creatinine, albumin.

Primary hyperparathyroidism and neoplasia especially lung, breast (with metastases to bone) account for over 90% of cases.

Diabetes insipidus

Impaired secretion of vasopressin (antidiuretic hormone) from the posterior pituitary leads to polyuria, nocturia and compensatory polydipsia resulting in the passage of 3 to 20 L of dilute urine per day. There are several causes of diabetes insipidus (DI), the commonest being postoperative (hypothalamic-pituitary) which is usually transient only. Other causes of cranial DI include congenital tumours, infections and infiltrations. In nephrogenic DI the renal tubules are insensitive to vasopressin. Differential diagnoses include compulsive (psychogenic) water drinking and the syndrome of secretion of inappropriate antidiuretic hormone (SIADH), which is caused by cancer (e.g. lung, lymphomas, kidney, pancreas), pulmonary disorders, various intracranial lesions and drugs such as carbamezepine and many antipsychotic agents. The treatment of DI is desmopressin, usually given twice daily intranasally.

Hypoparathyroidism

Hypoparathyroidism, which is uncommon, causes hypocalcaemia. Causes include congenital deficiency (di George's syndrome), idiopathic (autoimmune) hypoparathyroidism and postoperative thyroidectomy and parathyroidectomy. The main features are neuromuscular hyperexcitability, tetany and neuropsychiatric manifestations.

Two important signs of hypocalcaemia are Trousseau's sign and Chvostek's sign.

Treatment involves careful adjustments in dosage of calcitriol and calcium to correct hypocalcaemia and avoid hypercalcaemia (the latter may lead to renal impairment).

References

1. Fry J. Common diseases (4th edn). Lancaster: MTP Press Limited, 1985, 358-361.

2. Stockigt J, Topliss DJ. Hypothyroidism. In: MIMS Disease Index (2nd edn). Sydney: IMS Publishing, 1996, 267-269.

3. Yuen R. Common thyroid conditions. Current therapeutics, 1992; 10:23-29.

4. Yuen R. Endocrinology 1. RACGP: CHECK Programme, unit 243,1992, 2-5.

5. Hales I. Thyrotoxicosis. In: MIMS Disease Index. Sydney: IMS Publishing, 1991-92, 541-543.

6. Moulds RFW. Therapeutic guidelines: Endocrinology. Melbourne: Therapeutic Guidelines Limited, 1997,

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