Delayed recurrent SIADH associated with SSRIs

BACKGROUND: Depression is a common problem in elderly patients and is frequently treated with selective serotonin-reuptake inhibitors (SSRIs). OBJECTIVE: To report a case of delayed recurrent hyponatremia after switching from one SSRI to another. CASE SUMMARY: An 87-year-old depressed woman began treatment with fluvoxamine. One week later, she was diagnosed with hyponatremia, most likely syndrome of inadequate antidiuretic hormone. Following discontinuation of fluvoxamine, the serum sodium concentration normalized. Later, she began treatment with paroxetine. Sixteen months after initiating paroxetine, she developed symptomatic recurrent hyponatremia. After paroxetine was discontinued, the sodium concentration normalized. DISCUSSION: In this case, unlike those previously reported, hyponatremia recurred 16 months after a different SSRI was initiated. The Naranjo probability scale indicates a probable relationship between recurrent hyponatremia and paroxetine. The mechanism of SSRI-induced hyponatremia is multifactorial. CONCLUSIONS: This case illustrates that replacement of one SSRI with another can cause delayed, recurrent hyponatremia in elderly patients. Plasma sodium concentrations must be monitored, not only in the first weeks of treatment, but throughout the full course.