A sense of schizophrenia

Marker: A study finds that detecting olfactory deficiency can lead to early diagnosis of the mental illness that affects 2 million Americans.

Medicine & Science

November 17, 2003|By David Kohn | David Kohn,SUN STAFF

A new study has found that a faulty sense of smell may predict precisely the risk of schizophrenia, months or years before obvious symptoms appear.

Until now, doctors have had no reliable way to make an early diagnosis of the debilitating mental illness, which afflicts more than 2 million Americans.

"This is the first time we've found a potential marker specifically for schizophrenia. It's a promising diagnostic tool," said University of Melbourne neuropsychologist Dr. Warrick Brewer, one of the study's co-authors.

Early detection of schizophrenia can be key, Brewer said, because schizophrenic patients who get prompt treatment generally do better in the long run. A psychotic episode can cause permanent brain damage, increasing the chance of subsequent attacks. So catching the illness early can reduce later problems.

Published in The American Journal of Psychiatry, the study examined 81 people at high risk for developing schizophrenia. The subjects had all shown early subtle signs of the disease: genetic risk, disorganized thinking, or subtle hallucinations or delusions.

Brewer and his colleagues gave this group a standard 40-item scratch-and-sniff test, which asks subjects to smell an odor and then identify it. The smells included bubble gum, gasoline, lemon and licorice.

Twelve of the 81 subjects scored very low on the smell test. Over the next two years, only those 12 developed schizophrenia. Ten other patients also had psychotic episodes, but their symptoms were caused by mental illnesses other than schizophrenia.

Schizophrenia researchers praised the study. "The fact that they could use olfaction to differentiate schizophrenia, that's a very exciting finding. It could provide an early warning system," said University of Pennsylvania psychiatrist Dr. Bruce Turetsky, who also studies the connection between smell and schizophrenia. Turetsky has found that nasal cavities of schizophrenics are smaller than those of healthy subjects.

Scientists have known for a decade that those with the disease have an impaired sense of smell. Most people with schizophrenia can perceive the presence of a strong odor but have trouble recognizing and naming it. They might mistake the scent of pizza for that of bubble gum.

Scientists suspect that this olfactory deficiency arises from a quirk in neural circuitry: The area of the brain that interprets emotion and social signals also decodes aroma.

In people with schizophrenia, this brain region, the limbic system, somehow malfunctions. Those with the disease are often detached and withdrawn, and have trouble decoding social and emotional signals. This limbic breakdown also damages the ability to label odor, and the impairment seems to precede other symptoms, providing an early clue to the disease.

"Even before the onset of schizophrenia, these people were showing a compromise of that neural pathway," Brewer said. But he stressed that not everyone with a poor sense of smell has a higher chance of getting schizophrenia. Only those who also show other symptoms are at greater risk, he said.

The study adds to the growing awareness that studying smell can help researchers understand schizophrenia, according to Columbia University psychiatry professor Dr. Dolores Malaspina, who also does research on the subject. She recently found the most socially withdrawn schizophrenic patients have the most impaired sense of smell.

"Smell is something that we can look at so easily, and yet it tells us so much," she said. "It is a window into the functioning of the emotional brain."

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