SIADH and hyponatraemia

Question 1

Definition

Answer 1

“Syndrome of inappropriate ADH”
- Excessive release of ADH
- From posterior pituitary or non-pituitary source

• Cause of hyponatraemia

Causes
- CNS
- Neoplastic
- Lung disease
- Drugs
- Mutations
- Micellaneous

Question 2

CNS causes of SIADH (8)

Answer 2

Head trauma
- Subarachnoid bleed
- Subdural haematoma

CNS mass

Infections
- Meningitis, encephalitis, abscess, AIDS

Hydrocephalus

Guillain-Barre

MS

Porphyria

Question 3

Neoplastic causes of SIADH

Answer 3

Carcinomas
- Lung
- GI
- GU

Lymphoma

Sarcoma

Question 4

Pulmonary causes of SIADH

Answer 4

Infection
- Pneumonia
- Abscess

Asthma

CF

Question 5

Drugs that can cause SIADH (8)

Answer 5

Carbamazepine

SSRIs,

Tricyclics: Amitriptyline

Chlorpropamide

Oxcarbazepine

Valproic acid

MDMA

Morphine

Question 6

Signs and symptoms of SIADH
- GI
- MSK
- Neuro

Answer 6

GI (common)
- Anorexia
- Nausea
- Vomiting

Neuro
- Altered mental status
- Lethargy
- Seizures
- Headaches

MSK
- Aches and generalised weakness

Question 7

Diagnosis

Answer 7

Serum sodium= hyponatraemia
- <125

Serum osmolality= low
- <260 mmol/kG

Urine osmolality

Absence of
- Hypovolemia
- Oedema
- Diuretics

Question 8

Treatment of SIADH

Answer 8

1. Treat underlying cause
2. Fluid restriction + IV hypertonic saline
3. Furosemide to increase water excretion, especially if at risk of fluid overload
4. Vaptan- increases urine output
5. Demeclocycline
   - Antibiotic that causes diminished responsiveness of the collecting tube to AVP

Question 9

Differentials for SIADH

Answer 9

Addison’s disease

Hypovolaemia
- Urine sodium is low
- Central venous pressure <8

Hypervolaemia

Psychogenic polydipsia

Hypothyroidism