Hyponatremia, hyperkalemia, and other fluid and electrolyte disturbance recognition and mechanisms tested on USMLE Step 1.
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- What serum sodium level defines hyponatremia?
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Less than 135 mEq/L- What are the three volume status categories used to classify hyponatremia?
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Hypovolemic, euvolemic, and hypervolemic- What hormone is inappropriately elevated in SIADH?
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Antidiuretic hormone (ADH/vasopressin)- In SIADH, urine osmolality is ____ despite a low serum osmolality.
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inappropriately concentrated- Name a classic paraneoplastic cause of SIADH.
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Small cell lung cancer- What is the first-line treatment for chronic SIADH?
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Fluid restriction- What serious neurologic complication can result from correcting hyponatremia too quickly?
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Osmotic demyelination syndrome (central pontine myelinolysis)- What is the maximum safe rate of sodium correction in chronic hyponatremia?
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About 8 mEq/L per 24 hours- What clinical picture is characteristic of osmotic demyelination syndrome?
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Spastic quadriparesis, dysarthria, and dysphagia, resembling locked-in syndrome- In euvolemic hyponatremia, how does urine osmolality distinguish primary polydipsia from SIADH?
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Primary polydipsia has dilute urine (low urine osmolality); SIADH has concentrated urine- How does cerebral salt wasting differ from SIADH in volume status?
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Cerebral salt wasting causes hypovolemia; SIADH causes euvolemia- What are the predominant symptoms of severe hyponatremia?
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Neurologic symptoms such as confusion, seizures, and cerebral edema- What lab abnormality can cause spurious pseudohyponatremia?
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Severe hyperlipidemia or hyperproteinemia- What causes translocational hyponatremia?
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Severe hyperglycemia pulling water into the extracellular space- By how much does serum sodium fall for every 100 mg/dL rise in glucose above normal?
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About 1.6 mEq/L
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