SIADH = Syndrome of inappropriate antidiuretic hormone secretion
Important cause of HYPOnatraemia
Diagnosis requires
- Presence of
- HYPOnatraemia
- Euvolaemia (normovolemia)
- High urinary sodium (>20 mmol/L)
- Urine osmolality > plasma osmolality
- Serum osmolality <280 mmol/kg (hypotonic HYPOnatremia)
- Urine osmolality >500mmol/kg (inappropriately concentrated)
- Absence of
- Abnormal renal, cardiac, thyroid, adrenal hepatic function
- Hypervolaemia (oedema)
- NOT on a diuretic
Cause
- Malignancy
- Small cell lung, pancreas, prostate, leukaemia, cervical
- Central Nervous System (CNS)
- Tumour
- Trauma (Head injury, SAH, SDH)
- Infection (encephalitis, abscess)
- Vascular (CVA, aneurysm, vasculitis)
- Other (GBS, MS, DT)
- Respiratory
- Tumour
- Infection (aspergillosis, pneumonia, abscess)
- COPD, CF
- Drugs
- Opiates
- Psychotropic (TCA, MAOI, SSRI)
- Cytotoxic, chemotherapeutic
Correction
- Corrected with water restriction 500-1000ml/day
- Does not respond to Na replacement
References and Links
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CCC Differential Diagnosis Series
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NEURO
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Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
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RESP
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Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
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CVS
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Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
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GIT
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Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
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GUT
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Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
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MSK
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Arthritis, Shoulder pain, Wasting of the small muscles of the hand
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DERM
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Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
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ENDO
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Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
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HAEM
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Splenomegaly
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PAEDS
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Floppy infant
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MISC
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Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
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IMAGING
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CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR,
ABDO: Gas on abdominal X-ray, Kidney mass,
BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly,
OTHER: Pseudofracture on X-Ray,
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LABS
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LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,
HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,
ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis,
Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes
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Cite this article as: Mike Cadogan, "SIADH DDx," In:
LITFL - Life in the FastLane, Accessed on March 29, 2023,
https://litfl.com/siadh-ddx/.
Associate Professor Curtin Medical School, Curtin University. Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM Sir Charles Gairdner Hospital. Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |
