Syndrome of Inappropriate Antidiuretic Hormone Secretion Flashcards
What is SIADH?
SIADH is a condition characterised by excessive release of antidiuretic hormone (ADH), leading to water retention, dilutional hyponatraemia, and low serum osmolality.
What are the main symptoms of SIADH?
Symptoms include nausea, vomiting, headache, confusion, seizures, and in severe cases, coma due to hyponatraemia.
What causes SIADH?
Causes include malignancies (e.g., small-cell lung cancer), CNS disorders (e.g., stroke, trauma), pulmonary conditions (e.g., pneumonia), and certain medications.
What is the pathophysiology of SIADH?
Excessive ADH secretion causes increased water reabsorption in the kidneys, leading to dilutional hyponatraemia and reduced serum osmolality.
How common is SIADH?
SIADH is a relatively common cause of hyponatraemia, particularly in hospitalised patients.
What are the risk factors for SIADH?
Risk factors include malignancies, CNS diseases, pulmonary disorders, and the use of medications such as SSRIs, antipsychotics, and chemotherapy agents.
What clinical examination findings might suggest SIADH?
Findings may include confusion, reduced consciousness, and signs of hyponatraemia such as seizures or coma in severe cases.
What investigations are used to diagnose SIADH?
Investigations include serum osmolality, urine osmolality, urine sodium levels, and exclusion of other causes of hyponatraemia (e.g., thyroid or adrenal dysfunction).
What is the typical serum osmolality in SIADH?
Low serum osmolality (<275 mOsm/kg) due to water retention.
What is the typical urine osmolality in SIADH?
Inappropriately high urine osmolality (>100 mOsm/kg) despite low serum osmolality.
What is the typical urine sodium concentration in SIADH?
Urine sodium concentration is typically >30 mmol/L due to euvolaemia.
What are the main differential diagnoses for SIADH?
Differential diagnoses include heart failure, cirrhosis, nephrotic syndrome, hypothyroidism, and adrenal insufficiency.
How is SIADH diagnosed?
Diagnosis is based on the criteria of hyponatraemia, low serum osmolality, high urine osmolality, and absence of other causes of hyponatraemia.
How does SIADH cause hyponatraemia?
Excess ADH leads to water retention, diluting serum sodium levels and causing hyponatraemia.
What malignancies are commonly associated with SIADH?
Small-cell lung cancer is the most commonly associated malignancy.
What is the role of brain imaging in SIADH?
Brain imaging is performed to rule out CNS causes of SIADH, such as stroke, infection, or trauma.
What is the initial management of severe hyponatraemia in SIADH?
Severe hyponatraemia is managed with hypertonic saline infusion under close monitoring to avoid rapid correction.
What is the role of fluid restriction in SIADH management?
Fluid restriction is the first-line treatment to reduce water intake and correct hyponatraemia.
What medications are used in the treatment of SIADH?
Medications include vasopressin receptor antagonists (e.g., tolvaptan), demeclocycline, and urea in refractory cases.
Why is rapid correction of hyponatraemia in SIADH dangerous?
Rapid correction can cause osmotic demyelination syndrome, leading to severe neurological damage.
How does SIADH differ from other causes of hyponatraemia?
SIADH is characterised by euvolaemic hyponatraemia, unlike hypovolaemic or hypervolaemic states seen in other causes.
What lifestyle adjustments are recommended for patients with SIADH?
Patients should adhere to fluid restrictions and avoid excessive fluid intake.
How can SIADH be prevented?
Prevention involves managing underlying conditions, avoiding triggering medications, and monitoring at-risk patients.
What is the role of demeclocycline in SIADH management?
Demeclocycline reduces kidney sensitivity to ADH, promoting water excretion and correcting hyponatraemia.
What is the prognosis for patients with SIADH?
Prognosis depends on the underlying cause; addressing the cause and managing hyponatraemia usually results in good outcomes.
