SIADH

Question 1

what produces and secretes ADH?

Answer 1

produces- hypothalamus

secreted- posterior lobe of the pituitary

Question 2

what is SIADH?

Answer 2

-a condition where there are inappropriately large amounts of ADH secreted

Question 3

what does excessive ADH result in?

Answer 3

• excessive water reabsorption in the collecting ducts
• this dilutes the sodium in the blood so you end up with a low sodium concentration (hyponatraemia)
• this excessive water reabsorption is not usually significantly enough to cause a fluid overload, therefore you end up with a ‘euvolaemic hyponatraemia’
• the urine becomes more concentrates as less water is excreted by the kidneys therefore patients with SIAD have a high ‘urine osmolality’ and ‘high urine sodium’

Question 4

what are the symptoms of SIADH?

Answer 4

• headache
• fatigue
• muscle aches and cramps
• confusion
• severe hyponatramia can cause seizure and reduced conscioussness
• hyponatraemia
• high urine osmolality/ high sodium levels in urine

Question 5

what can cause SIADH?

Answer 5

• post operative from surgery
• infection, particularly atypical pneumonia and lung abscesses
• medications (thiazide diuretics, SSRIs, NSAIDs, carbamazepinem vincristine, cyclophosphamide)
• malignancy (SMALL CELL CANCER)
• meningitis
• head injury

Question 6

how is SIADH diagnosed?

Answer 6

• diagnoses of exclusion
• clinical exam showing euvolaemia
• U+Es showing hyponatraemia
• urine sodium and osmolality will be high

Other causes of hyponatraemia excluded:

• negative short synacthen test to exclude adrenal insufficiency
• no history of diuretic use
• no diarrhoea, vomiting, burns, fistula or excessive sweating
• no excessive water intake
• no chronic kidney disease or acute kidney injury