SIADH Flashcards
What are causes of SIADH?
- Malignancy - SCLC, thyroid, prostate
- ADH secretion (ectopic)
- Drugs - SSRIs, ecstasy
- CNS disease - meningencephalitis, abscess, subdural/subarachnoid, head injury, neurosurgery, Guillain barre
- Hormone deficiency - hypothyroidism, adrenal insufficiency
- Other - porphyria, trauma, major abdo/thoracic surgery, HIV
- Pulmonary - TB, pneumonia, abscess, aspergillosis, SCLC
What would you consider as the likely cause of euvolaemic hypovolaemia if someone had a urine Na+ > 20 mmol/L?
SIADH likely
What investigations would you do if you suspected SIADH?
- Investigate underlying causes
- Review medications
- Consider CT head/Chest/Abdo/Pelvis
What criteria are required for the diagnosis of SIADH?
- Hypoosmolar hyponatremia
- Urine osmolality > plasma osmolality
- Urine sodium excretion > 20mmol/L
- Normal renal, hepatic, cardiac, pituitary, adrenal and thyroid function
- Absence of hypotension, hypovolemia, oedema and ADH-influencing drugs
- Hyponatremia corrects with water restriction
What plasma osmolality is commonly seen in SIADH?
<260 mmol/L
How would you manage someone with a electrolyte free water clearence of < 0.5 who had SIADH?
1 L fluid restriction, and reassess after 24-48 hrs
How would you manage someone with an electrolyte free water clearence of 0.5-1.0 in someone with SIADH?
0.5 L fluid restriction, and reassess after 24-48 hrs
How would you manage someone with a electrolyte free water clearence ratio of >1.0?
No fluid restriction
What would you want to calculate before determiningn how to treat SIADH?
Furst formula (electrolyte free water clearence)
What treatments would you consider using for someone with SIADH?
- Fluid Restriction
- Tolvaptan
- Demecocycline
- Urea oral
- Loop diuretics
- Lithium
Describe the basic concept of SIADH
Syndrome of inappropriate ADH secretion is a situation where the ADH hypersecretion is… inapropriate… in contrast to all the other situations where it might be elevated “appropriately”. Now, one must acknowledge that a raised ADH level is a perfectly reasonable response to hypovolemia, but it is difficult to use the word “appropriate” to describe ADH elevation in states of apparent volume depletion such as cirrhosis, congestive cardiac failure or myxoedema.
As one might imagine, elevated vasopressin levels tend to result in water retention, and a dilutional hyponatremia develops.
What are ectopic sources of ADH production?
- SCLC
- Leukaemia
- Lymphoma
- Thymoma
- Neuroendocrine tumours
- Pancreatic adenocarcinoma
What CNS disorders can cause SIADH?
- Cerebral trauma
- Brain tumour (primary or secondary)
- Meningitis or encephalitis
- Brain abscess
- Subarachnoid haemorrhage
- Acute intermittent porphyria
- Guillain–Barré syndrome
- SLE
What pulmonary disorders can cause SIADH?
- Pneumonia
- Tuberculosis
- Lung abscess
