Mortality over a 20-year period in patients with primary polydipsia associated with schizophrenia: a retrospective study.

Primary polydipsia, excessive fluid intake without medical cause, is present in over 20% of seriously and persistently ill psychiatric inpatients. The long-term effects of primary polydipsia on longevity have not previously been examined. Inpatients in a psychiatric hospital were screened for polydipsia in 1985. Those identified to be polydipsic, the majority of whom suffered from schizophrenia, were re-evaluated in 2005 and compared with a control group of non-polydipsic patients. Chart reviews were conducted and follow-up data were obtained. Of 172 patients at the time of screening, 48 suffering from schizophrenia either had or went on to develop polydipsia; 42 non-polydipsic patients with schizophrenia from the original survey were randomly selected as controls. Primary polydipsia had a significant negative effect on longevity. The median age at death (age at which 50% of cases have died) was 59 years for polydipsic patients and 68 for non-polydipsic control patients. Adjusting for duration of schizophrenia, smoking, and diagnosis, a patient with polydipsia had a 74% greater chance of dying before a non-polydipsic patient (a hazard ratio of 2.84 [95% Confidence Interval (CI): 1.22-6.64]). Outcome was worst in patients with severe polydipsia: the median age at death was 57 years and a patient with severe polydipsia had a 75% greater chance of dying before a non-polydipsic patient (hazard ratio of 3.36 [95% CI: 1.31-8.60]). When polydipsia is associated with schizophrenia, mortality is increased in comparison to that in patients with schizophrenia who do not drink water to excess.