Syndrome of inappropriate secretion of ADH

Question 1

What is SIDH

Answer 1

When excess ADH is secreted

Question 2

Define causes and risk factors for SIDH

Answer 2

Malignancy
Small cell lung carcinoma most common
Prostate
Thymus
Pancreas
Drugs
Opiates
Chlorpropamide
Carbamazepine
Vincristine
Brain issues
Meningitis
Cerebral abscess
Head injury
Tumour
Lung
Pneumonia
TB
Abscesses
Asthma
CF
Metabolic
Porphyria - group of very rare metabolic disorders that occur when the body can’t produce Haem
Alcohol withdrawal

Question 3

What is the pathology for SIDH to occur?

Answer 3

Excess ADH 🡪 insertion of aquaporin 2 increases 🡪 water retention 🡪 dilution of blood plasma 🡪 hyponatraemia
BUT ALSO
Excess ADH 🡪 insertion of aquaporin 2 increases 🡪 water retention 🡪 decreased RAAS – aldosterone 🡪 secretion of Na+ 🡪 excess water being excreted WITH Na+ (body is removing sodium from blood that already has a low concentration of sodium) 🡪 NORMOVOLAEMIC yet HYPONATRAEMIC

Question 4

What are the signs of SIDH

Answer 4

• Concentrated urine

- Mild dilutional hyponatraemia: could lead to fits and coma

Question 5

Describe the symptoms of SIDH

Answer 5

• Reduction in GCS and confusion with drowsiness
• Irritability
• Headache
• Anorexia
• Nausea

Question 6

Describe the investigations and diagnosis for SIDH

Answer 6

• ECG: normal

- High urine osmolarity and low serum osmolarity

Question 7

What is the treatment and management for SIDH

Answer 7

Treat underlying cause
Restrict fluid – to increase Na+ concentration
Demeclocycline – inhibits action of vasopressin on kidney i.e. causes nephrogenic DI
Vasopressin receptor antagonists (vaptans) – V2 blocker
Tolvaptan – used for treatment of hyponatraemia secondary to SIADH as promotes water excretion with no loss of electrolytes
Oral furosemide – salt and loop diuretics if severe and to prevent circulatory overload