Epidemiology, Symptoms, and Treatment Characteristics of Hyponatremic Psychiatric Inpatients

Hyponatremia is a common phenomenon in psychiatry occurring as an
adverse effect to drugs or following polydipsia. We performed a
retrospective in-depth analysis of hyponatremia cases in a large
unselected population of psychiatric inpatients. During a 3-year
period, all cases of hyponatremia were identified among patients
admitted to a large psychiatric state and university hospital by
the institution's electronic laboratory database. Demographic,
treatment-related, and laboratory data were obtained by consecutive
chart review, respectively. Hyponatremia occurred in 347 (4.9%) of
7113 cases, of which the majority (78%) displayed only a mild
manifestation. Symptoms were recorded in 28.8% of cases, already
occurred in mild forms, and comprised gait impairment (45%,
including falls), confusion (30%), sedation (26%), and dyspepsia
(41%). Age, female sex, nonpsychiatric drug
polypharmacy-particularly with thiazides and/or
angiotensin-converting enzyme inhibitors-and diagnosis of a mood
disorder were associated with more severe hyponatremia,
respectively. The proportion of hyponatremic patients treated with
venlafaxine, trazodone, carbamazepine, oxcarbazepine, and
first-generation antipsychotics, respectively, was significantly
higher in the hyponatremia sample than in the normonatremic
population. This was, surprisingly, not the case with selective
serotonin reuptake inhibitors or any other antidepressant drug
class. We found prescription with second-generation antipsychotics
to be significantly associated with less severe hyponatremia.
Hyponatremia may be mainly attributed to the syndrome of
inappropriate antidiuretic hormone secretion, as indicated by
decreased serum osmolarity in our sample. Besides old age and
female sex, treatment with certain drugs-rather than whole drug
classes-carries a substantially increased risk.