SIADH
OVERVIEW
Syndrome Of Inappropriate ADH secretion (SIADH) is hyponatraemia due to an increase in concentration of ADH inappropriate to the current osmotic or volume status. The differential diagnosis includes ADH analogues
DIAGNOSTIC CRITERIA
- hypotonic hyponatraemia
- urine osmolality > plasma osmolality (<275mOsm/kg) (i.e. concentrated urine despite hypotonic blood)
- urinary Na+ > 20mmol/L
- normal renal, hepatic, cardiac, pituitary, adrenal and thyroid function
- euvolaemia (absence of hypotension, hypovolaemia, and oedema)
- correction by water restriction
CAUSES (MAD CHOP)
Major Surgery
- abdominal
- thoracic
- transsphenoidal pituitary surgery (6-7 days post op)
ADH production by tumours (Ectopic)
- small cell bronchogenic carcinoma
- adenocarcinoma of pancreas/duodenum
- leukaemia
- lymphoma
- thymoma
Drugs
- antidepressants (e.g. SSRI, TCAs, MAOIs)
- psychotropics (e.g. haloperidol, chlorpromazine), carbamazepine, Na+ valproate)
- anaesthetic drugs (barbiturates, inhalational agents, oxytocin, opioids)
- ADH analogues (vasopressin, DDAVP)
- chemotherapy (e.g.Vinca alkaloids, Melphalan, Methotrexate and cyclophosphamide)
- others (e.g. NSAIDs, amiodarone, ciprofloxacin, morphine, MDMA, proton pump inhibitors)
CNS Disorders
- cerebral trauma
- brain tumour (primary or metastases)
- meningitis/encephalitis
- brain abscess
- SAH
- acute intermittent porphyria
- SLE
Hormone deficiency
- hypothyroidism
- adrenal insufficiency
Others
- Guillain-Barre Syndrome
- HIV infection (early symptomatic or AIDS)
- hereditary SIADH
- giant cell arteritis
- idiopathic (occult small cell or olfactory neuroblastoma)
Pulmonary Disorders
- pneumonia (viral, fungal, bacterial)
- TB
- lung abscess
MANAGEMENT
- see hyponatraemia document
- fluid restrict
- incremental increase in Na+ if indicated to avoid central pontine myelinolysis
- medications to decrease ADH secretion
- Demeclocycline
- Tolvaptan / Conivaptan
References and Links
- CCC – Hypernatraemia
- CCC – Hypernatraemia Mind map (PDF)
- CCC – Hyponatraemia
- CCC – Hyponatraemia Mind map (PDF)
- CCC – Hyponatraemia Interpretation (PNG)
- CCC – SIADH – SIADH DDx
- CCC – Diabetes Insipidus Central – Diabetes Insipidus DDx
- Case – Exercise-associated Hyponatremia
- Case – Seizures, hyponatremia and ADH
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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