SIADH Flashcards
Define SIADH
Characterised by continued secretion of ADH, despite absence of normal stimuli for secretion (i.e. increased serum osmolality or decreased blood volume)
Aetiology of SIADH
5 groups
Brain Lung Tumours Drugs Metabolic
Aetiology of SIADH - brain
6
Haemorrhage/thrombosis Meningitis Abscess Trauma Tumour Guillain-Barre syndrome
Aetiology of SIADH - lung
3
Pneumonia
TB
Other: abscess, aspergillosis, small cell carcinoma
Aetiology of SIADH - tumours
4
Small cell lung cancer
Lymphoma
Leukaemia
Others: pancreatic, prostate, mesothelioma, sarcoma, thymoma
Aetiology of SIADH - drugs
4
Vincristine
Opiates
Carbamazepine
Chlorpropamide
Aetiology of SIADH - metabolic
2
Porphyria
Alcohol withdrawal
Epidemiology of SIADH
prevalence x2
Hyponatraemia is MOST COMMON electrolyte imbalance seen in hospital
<50% of severe hyponatraemia is caused by SIADH
Presenting symptoms of SIADH
10
Mild hyponatraemia may be ASYMPTOMATIC Headache N/V Muscle cramp/weakness Irritability Confusion Drowsiness Convulsions Coma Symptoms of underlying cause
Signs of SIADH on physical examination
4
MILD hyponatraemia - no signs
SEVERE hyponatraemia
reduced reflexes
extensor planta reflexes
Signs of underlying cause
Investigations for SIADH - things to check
5
Low serum sodium
Creatinine (check renal function)
Glucose, serum protein & lipids - to rule out pseudohyponatraemia
Free T4 & TSH - hypothyroidism can cause hyponatraemia
Short synacthen test - adrenal insufficiency can cause hyponatraemia
Investigations for SIADH - diagnosis
6
Low plasma osmolality
Low serum Na+ concentration
High urine osmolality
High urine Na+
AND absence of hypovolaemia, oedema, renal failure, adrenal insufficiency & hypothyroidism
Investigations for cause (e.g. CXR, CT, MRI)
Define Pseudohyponatraemia
Na concentration is actually normal but is erroneously reported as low because of presence of either hyperlipidaemia or hyperproteinaemia
Management of SIADH
4
Treat underlying cause
Fluid restriction
Vasopressin receptor antagonists (e.g. tolvaptan)
In SEVERE cases - slow IV hypertonic saline & furosemide w/ close monitoring
Complications of SIADH
4
Convulsions Coma Death Central pontine myelinolysis - occurs w/ rapid correction of hyponatraemia Characterised by: quadriparesis respiratory arrest fits
