Calcium Metabolism

22/07/2013 by admin | Endocrine
  1. Acute hypercalcaemia:
    1. o The more rapid the rise and the higher the level, the more likely the patient will present with an acute brain syndrome (=p/c: confusion, drowsiness, coma, muscle weakness, psychosis)
    2. o Hypercalcaemia in 5-50/10,000
    3. o In mild hypercalcaemia = p/c: thirst, polyuria (due to calcium induced nephrogenic diabetes insipidus), and also expect anorexia, N&V, abdo pain, constipation.
    4. o Chronic hypercalcaemia = renal stones and bone disease
  2. Aetiology:
  3. Is it due to malignancy?
    1. o Is the parathyroid hormone (PTH) level high/low?
    2. Normal (inappropriate in healthy parathyroid) or high PTH = primary hyperparathyroidism/tertiary hyperparathyroidism (autonomous parathyroid glands in longstanding chronic renal failure)/familial hypocalciuric or lithium-induced hypercalcaemia
    3. Low PTH = parathyroid gland is not responsible = malignancy, sarcoidosis, thyrotoxicosis, thiazide diuretic induced
    4. o Elevated alkaline phosphatase with deranged LFTs = malignancy
    5. o Paget’s disease = mild hypercalcaemia and large rise in alk phos
    6. o Multiple myeloma = hypercalcaemia and paraprotein on electrophoresis
    7. o Sarcoidosis = bilateral hilar lymphadenopathy on CXR
    8. o Need a full dietary/drug history for excess vit D or calcium containing antacids (milk-alkali syndrome). Thiazides and lithium.
    9. o Primary hyperparathyroidism:
    10. Most common cause of hypercalcaemia
    11. F>M (2>1), 90% are >50yo, 50% asymptomatic, symptoms are of hypercalcaemia.
    12. In 80% the pathology is caused by a single parathyroid adenoma – although occasionally diffuse hyperplasia of all four glands occurs
    13. Occasionally multiple endocrine neoplasia (MEN) I or II is present
    14. In young and all symptomatic patients, surgical resection of the parathyroid adenoma is definitive tx. If the operating surgeon cannot locate the adenoma – nuclear or USS can be used to locate it.
    15. Post-op hypocalcaemia is usually transient and is treated with calcium supplements and 1-alpha-hydroxy-vitamin D.
    16. o Hypercalcaemia of malignancy:
    17. 2nd most common cause of high Ca.
    18. Two underlying mechanisms:
    19. Tumour deposits in bone (95% of hypercalcaemia of malignancy is due to metastatic spread)
    20. Most common neoplasms are lung, breast and myeloma
    21. Patients are usually symptomatic from cancer and from high calcium.
    22. o Humoral hypercalcaemia of malignancy (HHM):
    1. Relates to PTH-related peptide (PTHrP), 144 AA in length, which bears a structural relationship with PTH and mimics its action. Typically produced by squamous carcinoma of the lung (less commonly of the GU system or gynae). HHM is rare – but key to know as not all patients with malignancy have metastatic disease!!
    2. o Sarcoidosis and other granulomatous diseases:
    3. Give a high calcium but usually respond well to steroids
    4. o Other causes of hypercalcaemia:
    5. Thyrotoxicosis and thiazide diuretics = high calcium
    6. o Familial hypocalciuric hypercalacemia is autosomal dominant inherited condition – associated with hypercalcaemia, and low renal extraction of calcium.
  1. Mx of hypercalcaemia:
    1. o Acute/symptomatic hypercalcaema is a medical emergency
    2. o Aggressive rehydration with physiological or 0.9% saline – which readily lowers calcium
    3. o Loop diuretics can be added once adequate hydration has occurred
    4. o Bisphosphonates are helpful regardless of underlying pathology
    5. o Steroids may be added in hypercalcaemia of malignancy and vit D related hypercalcaemia
    6. o Calcitonin helps in Paget’s disease. 
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