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
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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
Patients can be asymptomatic, or experience the following:
- oliguria
- volume expansion
- hyponatremic symptoms: nausea, vomiting, headache, seizure, coma
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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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