Endocrine Abstracts

Hyponatraemia is the commonest electrolyte abnormality in clinical practice; epidemiological data would suggest that SIAD is the commonest cause of hyponatraemia, and it is particularly important in patients undergoing neurosurgery, in whom SIAD is common. Recent data has shown that even mild hyponatraemia (plasma sodium 125–135 mmol/l) is associated with gait instability, falls, fractures, osteoporosis and increased mortality. This has led to the recognition that correct diagnosis and treatment of hyponatraemia may offer the opportunity to reduce morbidity an mortality and to reduce hospital stay. SIAD must be differentiated from other causes of hyponatraemia and the key diagnostic criteria are plasma osmolality <275 mOsm/kg, urine osmolality >100 mOsm/kg, euvolaemia, urine sodium >30 mmol/l and exclusion of hypothyroidism, glucocorticoid deficiency and diuretic use. It is particularly important to exclude acute ACTH/cortisol deficiency in patient with subarachnoid haemorrhage or traumatic brain injury. Fluid restriction is the traditional treatment for SIAD and still has a role, particularly in hospital patients with transient hyponatraemia, but there is a lack of an evidence base, and it is difficult for patients to maintain without close supervision. Randomised controlled trials have shown that the vasopressin receptor antagonists (vaptans) are superior to placebo in the management of hyponatraemia dur to SIAD and other causes; they cause an aquaresis, but in contrast to loop diuretics, no natriuresis. Tolvaptan is now available in oral form in Europe though cost remains a prescribing consideration, particularly in long term hyponatraemia