SUN-435 SIADH Precipitated by Pneumonia in a Background of Hypothyroidism and SSRI Use

Introduction: Hyponatremia is serum sodium levels below 135 meq/L. SIADH is a disorder of impaired water excretion caused by the inability to suppress the secretion of ADH leading to hyponatremia. Important causes of hyponatremia are heart failure, cirrhosis, diuretic induced, hypothyroids, cortisol deficiency and SIADH. Causes of SIADH are CNS disorders, malignancies, surgery, pulmonary disease (particularly pneumonia), hormone deficiency (both hypopituitarism, hypothyroidsm), HIV, drugs- esp. SSRIs. Clinical Case: 74 y/o F with past medical history of Diabetes, HTN, hypothyroidism, depression and chronic compensated hyponatremia under carvedilol, losartan, levothyroxine, citalopram, presented to ER with SOB with wheezing. Patient was admitted for pneumonia and treated with azithromycin and ceftriaxone. In Day 2, he developed intractable nausea and vomiting despite zofran and phenargan. IV NS was started. Patient developed hyponatremia, Na of 126 mEq/L, serum osmolality 240, Urine osm 457 mOsm/, TSH was 41 mIU/L. Levothyroxine was increased to 175 mcg. Fluid & Citalopram was stopped. Na was closely monitored. Over the next few days, patient and Na levels slowly improved with fluid restriction and Na tablets. Conclusion: Not all hyponatremia is SIADH while SIADH is a cause of hyponatremia. The diagnosis is often confusing. SIADH should be suspected in any patient with serum Na <135 mmol/L, serum osmolality <280 mOsm, and a inappropriate and relatively high urine osmolality (compared to serum osmolality). SIADH is more common in patients above age 65 years. Finding out the cause and fluid restriction is the mainstay of treatment in SIADH. Exception to this is brain surgeries & Sub Arachnoid Hemorrhage where there may be ongoing cerebral salt wasting and, fluid restriction can be deleterious as it can cause cerebral vasospasm. However for most cases of non-SIADH hyponatremia, Sodium chloride, (oral tablet or isotonic saline) is the therapy. Other ways to treat hyponatremia would be treating the underlying cause, restricting water intake or vasopressin receptor antagonist. For severe case (with seizure and severe neurological abnormalities) of any hyponatremia, intravenous hypertonic saline is the choice.