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A 74-year-old female with major depressive disorder was started on sertraline 50 mg daily three weeks ago by her primary care provider. She presents to the psychiatric clinic with complaints of increased fatigue, nausea, mild confusion, and unsteady gait that developed gradually over the past week. Her daughter reports that the patient seems 'more confused than depressed now.' Her medical history includes hypertension managed with hydrochlorothiazide 25 mg daily and osteoarthritis for which she takes ibuprofen as needed. Laboratory results reveal sodium 126 mEq/L, serum osmolality 264 mOsm/kg, urine osmolality 480 mOsm/kg, and urine sodium 58 mEq/L. Her sodium level was 139 mEq/L on routine labs drawn one month ago. Which assessment finding pattern is most consistent with SSRI-induced syndrome of inappropriate antidiuretic hormone secretion?
Explanation
SSRI-induced SIADH presents with the laboratory triad of hypotonic hyponatremia, inappropriately concentrated urine, and elevated urine sodium in a euvolemic patient. Risk factors include age over 65, female sex, and concurrent medications that impair free water excretion including thiazide diuretics and NSAIDs. Onset typically occurs within one to four weeks of SSRI initiation, and symptoms include fatigue, nausea, confusion, and gait instability.
Key Takeaway
SSRI-induced SIADH is characterized by hypotonic hyponatremia with inappropriately concentrated urine and elevated urine sodium, typically developing within one to four weeks of SSRI initiation, with elderly females on concurrent thiazides or NSAIDs at highest risk.