SIADH DDx

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

• CCC – Hypernatraemia
• CCC – Hypernatraemia Mind map (PDF)
• CCC – Hyponatraemia
• CCC – Hyponatraemia Mind map (PDF)
• CCC – Hyponatraemia Interpretation (PNG)
• CCC – SIADH
• CCC – Diabetes Insipidus Central
• Case – Exercise-associated Hyponatremia
• Case – Seizures, hyponatremia and ADH

CCC Differential Diagnosis Series
NEURO	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
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	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
GIT	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
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	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,
LABS	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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