Endocrinology: SIADH

Question 1

Outline the pathophysiology of SIADH

Answer 1

Too much ADH produced

Concentrated urine = Na>20mM, osmolality >500

Hyponatraemia or plasma osmolality <275

Absence of hypovolaemia, oedema or diuretics

Question 2

What are the causes of SIADH?

Answer 2

Surgery

Intracranial = meningitis, head injury

Alveolar = SCLC, pneumonia, TB

Drugs = haloperidol, SSRIs

Question 3

Outline the signs and symptoms of SIADH

Answer 3

Nausea or vomiting

Cramps or tremors

Depressed mood, memory impairment

Irritability

Personality changes, such as combativeness, confusion, and hallucinations

Seizures

Coma

Question 4

How should SIADH be investigated?

Answer 4

Must exclude endocrine and renal causes, make sure no diuretic use and normal K (MUST EXCLUDE ADDISON’S and HYPOTHYROIDISM) - measure random cortisol and TFTs

Serum/urine Na

Serum/urine osmolality

Urine output

Question 5

How should SIADH be managed?

Answer 5

Treat the cause

Fluid restrict

Vasopressin receptor antagonist = demeclocycline, vaptans (tolvaptan)