Metabolic

Question 1

Summary of SIADH

Answer 1

causes hyponatremia with low serum osmolality and concentrated urine (urinary sodium >40 mEq/L) with inappropriate urine osmolality (>100 mOsm/kg) levels.

In the setting of serum hypotonicity (serum osmolality <275 mOsm/kg), it is expected that the urine osmolality would be <100 mOsm/kg.

Question 2

Drug causes of SIADH

Answer 2

carbamazepine, sulfonylureas, SSRIs, tricyclics

Question 3

Summary of hypercalcaemia

Answer 3

The most common presenting features of which are dehydration, psychiatric manifestations and confusion, anorexia and constipation. Although hypercalcaemia can be secondary to hyperparathyroidism, sarcoidosis, hyperthyroidism, drugs (thiazide diuretics, vitamin D etc) or prolonged immobility etc, 90% of severe cases (>3.0 mmol/l) requiring admission are due to malignancy (as in this gentleman).

Question 4

Causes of hypophosphataemia

Answer 4

can be caused by diabetic ketoacidosis. A rise in insulin causes phosphate to shift into the intracellular compartment, similar to the mechanism involved in hypophosphataemia as a result of refeeding syndrome or hyperglycaemic hyperosmolar non-ketotic coma (HONK).

Phosphate replacement therapy is rarely required unless it is severe and should be given as an infusion.