SIADH Flashcards
What is SIADH?
Continued secretion of ADH, despite the absence of normal stimuli for secretion (i.e. increased serum osmolality or decreased blood volume)
List broad areas that when effected can lead to SIADH
Brain Lungs Drugs Tumours Metabolic state
List 6 “brain” related causes of SIADH
Haemorrhage/thrombosis Meningitis Abscess Trauma Tumour Guillain-Barre syndrome
What 4 pulmonary pathologies can lead to SIADH?
Pneumonia
TB
Abscess
Aspergillosis
What cancerous pathologies can lead to SIADH?
Small cell lung caner Breast cancer Lymphoma Leukaemia Pancreatic cancer Prostate cancer Mesothelioma Sarcoma Thymoma
List 4 drugs that may lead to SIADH
Vincristine
Opiates
Carbamazepine
Chlorpropamide
What metabolic states may lead to SIADH?
Porphyria
Alcohol withdrawal
Describe the epidemiology of SIADH
Hyponatraemia is the MOST COMMON electrolyte imbalance seen in hospital
< 50% of severe hyponatraemia is caused by SIADH
List 9 symptoms of SIADH
Headache N+V Muscle cramp/ weakness Irritability Confusion Drowsiness Convulsions Coma Symptoms of underlying cause
List signs of severe hyponatraemia
Reduced reflexes
Extensor plantar reflexes
Signs of underlying cause
What is the hyponatraemia caused by in SIADH?
Dilution from excessive water reabsorption + not due to a decrease in total body Na+
Why does SIADH cause a euvolaemic hyponatraemia?
Hypervolaemia causes heart distention, so BNP + ANP are secreted which cause salt+ water extcretion
What investigations are performed in suspected SIADH?
Serum sodium
Serum osmolarity
Serum urea
Urine osmolarity
Creatinine (check renal function)
Glucose, serum protein + lipids: to exclude pseudohyponatraemia
Free T4 + TSH: hypothyroidism can cause hyponatraemia
Short synACTHen test: adrenal insufficiency can cause hyponatraemia
What is Pseudohyponatraemia?
When Na+ concentration is actually normal but is erroneously reported as being low because of the presence of either hyperlipidaemia or hyperproteinaemia
Describe the results necessary for diagnosis of SIADH
Low plasma osmolality Low serum Na+ conc. High urine osmolality High urine Na+ \+ Absence of hypovolaemia, oedema, renal failure, adrenal insufficiency + hypothyroidism
List 3 investigations that may be used to identify the cause of SIADH
CXR
CT
MRI
Describe the management of SIADH
1st line: Treat underlying cause
1st line: Fluid restriction to 1L per day
2nd line: Vasopressin receptor antagonists (e.g. tolvaptan)
3rd line: NaCl + furosemide
4th line: demeclocycline
List 4 complications of SIADH
Convulsions
Coma
Death
Central pontine myelinolysis
What is the prognosis of SIADH?
Depends on the CAUSE
Na+ < 110 mmol/L is associated with a HIGH MORBIDITY + MORTALITY
50% mortality with central pontine myelinolysis
What is Central pontine myelinolysis? What is it caused by? What is it characterised by?
Demylination of pons Occurs with rapid correction of hyponatraemia Quadriparesis Respiratory arrest Fits
Describe the treatment of SIADH in severe/ acute cases
Slow IV hypertonic saline + furosemide with close monitoring
