Science / Medicine : Many Mental Patients Apparently Have Physiological Defect That Causes Thirst
Many psychiatric patients apparently have a physiological defect that makes them unusually thirsty and therefore highly susceptible to literally drinking themselves to death.
The defect seems to explain why at least some psychotic people are at increased risk for so-called water intoxication and may give researchers new insights into the biological basis of mental illness, researchers say.
“One of the major issues in psychiatry is tracking down the neurochemical basis of psychosis,” said Dr. Morris B. Goldman of the University of Chicago Medical Center.
“If you can start to get a handle on one of these associated phenomena, then we may get a better understanding of the neurophysiological basis of the psychosis,” Goldman said.
Between 5% and 10% of chronic psychiatric patients are believed to experience episodes of water intoxication, which results from the consumption of unusual amounts of water that the kidneys cannot get rid of. (Drinking large amounts of water is considered healthy; but to be considered excessive, a patient would have to consume more than 3 or 4 gallons of water on a daily basis.)
Excess water in the body dilutes salt levels, which can interfere with nerve cell function and cause confusion, seizures and even comas and death in some cases.
About 30% of chronic psychiatric patients drink excess amounts of water. The reason had been unclear, but it was believed to be possibly related to the drugs they took.
About one-third of the excessive drinkers suffer episodes of water intoxication. To determine whether there was a physiological basis for it, Goldman and his colleagues studied eight psychiatric patients who had experienced intoxication and compared them with seven who had not.
In a study published recently in the New England Journal of Medicine, the researchers found that the patients who had experienced intoxication apparently had a defect in their kidneys that prevented them from expelling enough of the excess water.
The eight patients who experienced intoxication could excrete only about half as much water as the other seven patients, Goldman said.
In addition, measurements of a hormone that regulates thirst, known as vasopressin, determined that the eight patients who experienced intoxication also became thirstier earlier, accounting for why they drank so much water.
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The findings are intriguing, because the part of the brain that controls vasopressin, and therefore thirst, also is believed to generate hallucinations and delusions the patients experience, he said.
Doctors have a good understanding of the mechanisms of thirst and if the excess thirst experienced by psychiatric patients is just another manifestation of their disease, it may help physicians understand the illness better, Goldman said.
“We have a reasonable understanding of the normal physiology of thirst and water intake and excretion,” said Goldman in a telephone interview.
The findings also indicate that the water intoxication that afflicts many psychiatric patients is not always self-induced, as many had believed, he said.
“This demonstrates a physiologic basis for what previously was called self-induced,” said Goldman.
