Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to SSRIs

A 74-year-old Caucasian male with previously diagnosed dementia, HLP, HTN, h/o seizures and major depressive disorder was admitted to the hospital from his nursing home with altered mental status and frequent falls. Per previous documentation, his seizures have been well-controlled on Dilantin over the past 20 years. Depression and dementia has been followed by psychiatry on a chronic basis. He is currently taking Abilify (aripiprazole) for delusions, and Cogentin (benztropine) was recently added with the thought that his frequent forward falls may be secondary to antipsychotic-related dyskinesia. Per nursing home staff, the patient does have a history of both bladder and bowel incontinence.

Dementia, HLP, HTN, h/o seizures and major depressive disorder

Aspirin, esomeprazole, phenytoin SR 300 mg cap po qd, simvastatin, valsartan, citalopram, Abilify, Ativan, Ambien

Physical examination:
VS: T 36.7-P 65-RR 20-BP 116/70-SpO2 92%
Alert, cooperative with the physical exam, in no acute distress
CV: RRR, normal S1 and S2. No murmurs, rubs, or gallops
Lungs: CTA (B), no wheezes, rales, or ronchi
Abdomen: Normoactive bowel sounds. Nontender and nondistended. No hepatosplenomegaly.
Extremities: No c/c/e
Neuro: Alert, oriented to person, place, and year. Repeats 3 objects but unable to recall after 5 minutes. Speech fluent without dysphasia.

Laboratory results:

BMP and other laboratory results in SIADH

Urine sodium and UA in SIADH

What happened?
UA, CXR and CBC were all normal. EEG did not show acute seizure activity. CT scan of the brain: Stable atrophy and chronic small vessel ischemic change.

All psychiatric medications were stopped. Psychiatry and neurology consults were called. SIADH work-up was ordered and the patient was placed on 1.5-liter fluid restriction. SIADH work-up includes: BMP, urine Na, plasma and urine osmolality, plasma uric acid, TSH.

What happened next?
Laboratory results confirmed typical SIADH.

Diagnostic criteria for SIADH include the following:
Hyponatremia (serum sodium less than 135 mEq/L)
Hypotonicity (plasma osmolality less than 280 mOsm/kg)
Inappropriately concentrated urine (more than 100 mOsm/kg water)
Elevated urine sodium concentration (more than 20 mEq/L), except during sodium restriction
Clinical euvolemia
Normal renal, adrenal, and thyroid function

Please compare the above criteria to the screenshot of our patient's laboratoy results shown above.

With fluids restriction, sodium level increased to normal and the patient was discharged to his nursing home. Citalopram was stopped.

Sodium level in SIADH

Final diagnosis:
Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to Selective Serotonin Reuptake Inhibitors (SSRIs)

Syndrome of Inappropriate Antidiuretic Hormone Secretion. eMedicine.
Hyponatremia. NEJM 2000.
Hypernatremia. NEJM 2000.

Created: 04/13/2007
Updated: 04/02/2008