Syndrome of Inappropriate Antidiuretic Hormone

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Introduction

Syndrome of Inappropriate Antidiuretic Hormone (SIADH) is a condition in which urine is inappropriately concentrated for the serum osmolality, with a high urine sodium.

 

 

 

The Case of...

a simple case introducing clincial presentation and calling for a differential diagnosis. To get students thinking.

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Causes and Risk Factors

SIADH can result from lung diseases such as pneumonia or abcesses, brain disease, or paraneoplastic symptoms of certain cancers such as SCLC, or as a side effect of certain medications.

common causes

  • post-operative state
  • stress, anxiety
  • pain
  • severe nausea

 

drugs

  • antidepressants: TCAs, SSRIs
  • antineoplastics: vincristine, cyclophosphamide
  • chlorpromazine
  • indapamide
  • amiodarone
  • opioids
  • clofibrate
  • general anaesthetics
  • DDAVP
  • oxytocin
  • nicotine
  • carbamazepine
  • chlorpromazine
  • barbituates

 

tumours

  • small cell lung cancer
  • bronchogenic carcinoma
  • pancreatic adenocarcinoma
  • hodgkin's disease
  • thymoma

pulmonary

  • pneumonia
  • abscess
  • tuberculosis
  • empyema
  • viral pneumonitis
  • acute respiratory failure
  • positive pressure ventilation

CNS

  • mass lesion
  • encephalitis
  • subarachnoid/subdural hemorrhage
  • stroke
  • head trauma/skull fracture
  • acute psychosis
  • acute intermittent porphyria

misc

  • HIV
  • multiple sclerosis
  • Guillain Barre syndrome

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Pathophysiology

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Signs and Symptoms

  • history
  • physical exam

History

Patients can be asymptomatic, or experience the following:

  • oliguria
  • volume expansion
  • hyponatremic symptoms: nausea, vomiting, headache, seizure, coma

Physical Exam

 

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Investigations

  • lab investigations
  • diagnostic imaging

Lab Investigations

bloodwork

  • electrolytes (low sodium)
  • creatinine
  • BUN
  • uric acid (often low)
  • TSH (to rule out hypothyroidism)
  • 8am cortisol (to rule out adrenal insufficiency)

urinalysis

  • osmolarity (increased >100, usually >300)
  • electrolytes (sodium increased)

 

Diagnostic Imaging

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Treatments

 Treat the underlying cause. 

Can fluid restrict and give salt (3% NaCl) if hyponatremic and symptomatic.

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Consequences and Course

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Additional Resources

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Topic Development

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