Pituitary: SIADH Flashcards
(10 cards)
What is the syndrome of inappropriate anti-diuretic hormone (SIADH)?
Increased release of ADH from the posterior pituitary gland, leading to increased water reabsorption and dilution of blood, causing hyponatraemia
SIADH results in a low sodium concentration in the blood.
What endocrine disorders cause
a) HYPERnatraemia
b) HYPOnatraemia
???
a) HYPERnatraemia = DI
b) HYPOnatraemia = SIADH
What are the symptoms of SIADH?
Symptoms vary with severity of hyponatraemia:
* Asymptomatic (if not severe)
* Headaches
* Fatigue
* Muscle aches and cramps
* Confusion
* Severe hyponatraemia may lead to seizures and reduced consciousness
Severity of symptoms correlates with the level of sodium in the blood.
Outline the physiology of ADH secretion in SIADH
What are common causes of SIADH?
3 x SSS:
Surgery - common post-op complication
SSRIs
Small Cell Lung Cancer - paraneoplastic syndrome
Other:
* Lung infections (atypical pneumonia, lung abscesses)
* Brain pathologies (head injury, stroke, intracranial hemorrhage, meningitis)
* HIV
The acronym SSS can help remember Surgery, SSRIs, and Small cell lung cancer as causes.
What is the diagnostic criteria for SIADH?
Diagnosis is based on:
* Euvolaemia (normal blood volume)
* Hyponatraemia (low sodium)
* High urine sodium
* High urine osmolality
It’s important to rule out other causes of hyponatraemia.
What tests help rule out other causes of hyponatraemia?
Tests include:
* Short synacthen test (exclude adrenal insufficiency)
* Checking for history of diuretic use
* Assessing for diarrhea, vomiting, burns, fistula, or excessive sweating
* Evaluating for excessive water intake
* Checking for chronic kidney disease (CKD) or acute kidney injury (AKI)
* Evaluating heart failure (HF) or liver disease
Primary polydipsia can also cause euvolaemic hyponatraemia but with low urine sodium and osmolality.
What initial steps are taken in the treatment of SIADH?
Initial treatment steps include:
* Establishing the cause (CXR, CT TAP, MRI head, drug history)
* Admission if symptomatic or severe (Na < 125 mmol/L)
* **Fluid restriction (750-1000 ml per day) **
* Vasopressin receptor antagonist (e.g., Tolvaptan)
Sodium concentration should not be changed more than 10 mmol/L in 24 hours.
What is a risk associated with treating severe hyponatraemia too quickly?
Osmotic Demyelination Syndrome (ODS)
ODS is a long-term complication that can occur when sodium levels are corrected too rapidly.
What is the treatment approach once Osmotic Demyelination Syndrome occurs?
Treatment is supportive, as there is a high risk of death and/or neurological deficit
Prevention is essential: sodium concentration should not be changed more than 10 mmol/L in 24 hours.
