SIADH

Question 1

What is SIADH?

Answer 1

A condition of inappropriate antidiuretic hormone secretion causing euvolemic, dilutional hyponatraemia

Question 2

What is the defining volume status in SIADH?

Answer 2

Euvolemic (no clinical signs of dehydration or fluid overload)

Question 3

What hormone is inappropriately elevated in SIADH?

Answer 3

Antidiuretic hormone (ADH, vasopressin)

Question 4

Where is ADH produced and stored?

Answer 4

Produced in the hypothalamus and stored in the posterior pituitary

Question 5

What is the primary renal action of ADH?

Answer 5

Increases water reabsorption in the collecting ducts

Question 6

Why does SIADH cause hyponatraemia?

Answer 6

Excess water retention dilutes serum sodium concentration

Question 7

Why do patients with SIADH not develop oedema?

Answer 7

Excess water is evenly distributed across body fluid compartments

Question 8

What happens to urine output in SIADH?

Answer 8

Decreased urine volume with inappropriately concentrated urine

Question 9

What happens to serum osmolality in SIADH?

Answer 9

Low serum osmolality

Question 10

What is the typical urine osmolality in SIADH?

Answer 10

Inappropriately high (>100 mOsm/kg) despite low serum osmolality

Question 11

What is the typical urine sodium concentration in SIADH?

Answer 11

High (>40 mmol/L)

Question 12

Why is urine sodium high in SIADH?

Answer 12

ADH-mediated water retention suppresses RAAS, promoting sodium excretion

Question 13

What malignancy is classically associated with SIADH?

Answer 13

Small cell lung cancer

Question 14

Which other cancers can cause SIADH?

Answer 14

Pancreatic and prostate cancer

Question 15

Which neurological conditions commonly cause SIADH?

Answer 15

Stroke, subarachnoid haemorrhage, subdural haemorrhage, CNS infection

Question 16

Which infections are classically linked to SIADH?

Answer 16

Tuberculosis and pneumonia

Question 17

Which drugs commonly cause SIADH?

Answer 17

SSRIs, tricyclics, carbamazepine, vincristine, cyclophosphamide

Question 18

Which antidiabetic drugs are associated with SIADH?

Answer 18

Sulfonylureas (glimepiride, glipizide)

Question 19

Which ventilation setting can precipitate SIADH?

Answer 19

Positive end-expiratory pressure (PEEP)

Question 20

What is the most important rule when correcting hyponatraemia in SIADH?

Answer 20

Correct sodium slowly to avoid central pontine myelinolysis

Question 21

What is the first-line management of SIADH?

Answer 21

Fluid restriction

Question 22

How does demeclocycline treat SIADH?

Answer 22

Reduces renal responsiveness to ADH

Question 23

What newer drug class is used to treat SIADH?

Answer 23

Vasopressin (ADH) receptor antagonists

Question 24

What serious complication results from rapid sodium correction?

Answer 24

Central pontine myelinolysis