Hyponatremia-induced change in mood mimicking late-onset bipolar disorder

Hyponatremia and bipolar disorder are rarely considered to have common features. This report describes a case of hyponatremia secondary to syndrome of inappropriate antidiuretic hormone secretion (SIADH) presenting as late-onset bipolar disorder and discusses the evidence linking hyponatremia to mood disorders.

Case report and review of published literature.

This case provides evidence that mood changes identical to those seen in bipolar disorder may be caused by hyponatremia at a variety of concentrations.

Further research is required to determine causes of SIADH in psychiatric patients with symptomatic hyponatremia and to elucidate the mechanism by which hyponatremia causes changes in mood. In older patients presenting with new-onset bipolar disorder, a physical etiology must always be excluded.