The unmasking of hidden severe hyponatremia after long-term combination therapy in exacerbated bipolar patients: a case series

Hyponatremia is occasionally unmasked in psychiatric patients during hospitalization after routine blood and urinary tests, and correlates in most cases with an inappropriate secretion of antidiuretic hormone, mainly due to iatrogenic factors. Only a few studies have regarded the combination of psychotropic drugs as triggers of chronic, asymptomatic hyponatremia in bipolar patients, who require to be hospitalized because of the exacerbation of their mental illness. We presented three clinical cases of patients affected by a long-term psychiatric disorder and under polypharmacotherapy for several months. After excluding other potential factors, we hypothesized that pharmacological treatment with a mood stabilizer (oxcarbazepine) associated with a benzodiazepine (delorazepam), a second-generation antipsychotic (olanzapine) or an antidepressant (fluvoxamine), triggered severe hyponatremia ([Na+] ≤125 mEq/L), serum hypo-osmolarity, and elevated inappropriate urine osmolarity added to more diluted sodium concentration. When we discontinued the treatment, clinical conditions of our patients improved, despite the previous administration of hypertonic saline jointly with water restriction. Psychiatrists should consider that bipolar patients on long-term polypharmacotherapy may present a higher risk of severe hyponatremia not clinically detectable. Consequently, routine laboratory tests should be periodically repeated as they represent the only available tool to unmask such electrolyte imbalances.