Intellectual Status Differentiates Mental Illness Risks

When it comes to intellectual, language, and behavioral performances, can adolescents who later develop bipolar disorder without psychosis be distinguished from adolescents who remain mentally healthy? The answer is no, a new study suggests.

The study, in fact, appears to be the first that has ever assessed the intellectual, language, and behavioral capabilities of young people who will later be diagnosed with bipolar disorder without psychotic symptoms.

The investigation was conducted by Michael Davidson, M.D., director of psychiatry at Chaim Sheba Medical Center in Tel-Hashomer, Israel, and colleagues and was reported in the December American Journal of Psychiatry.

What the researchers did, essentially, was use prospective, although historical, data provided by both the Israeli Draft Board Registry and Israel’s National Psychiatric Hospitalization Case Registry for their study.

First they focused on all adolescent Israelis who had been assessed by the draft board between 1985 and 1995. Then they zeroed in only on those adolescents who had no history of psychiatric illness and no sign of psychiatric illness at the time they were assessed by the draft board. Then they used the psychiatric hospitalization registry to determine which of these adolescents were subsequently hospitalized for schizophrenia, schizoaffective disorder, or nonpsychotic bipolar disorder. A total of 536 had been hospitalized for schizophrenia; 31 for schizoaffective disorder, and 68 for nonpsychotic bipolar disorder. On average, they had been hospitalized for these conditions when they were 20 or 21 years of age.

The investigators then matched each of these 635 subjects with an Israeli who had been assessed by the draft board at the same age, who had attended the same high school, and who did not appear in the psychiatric hospitalization registry during the follow-up period.

The scientists then compared draft board data about the intellectual, language, and behavioral abilities of the 635 subjects with draft board data about the intellectual, language, and behavioral abilities of the 635 controls. This way, they reasoned, they could determine how the mental and behavioral capabilities of the young people who later developed schizophrenia, schizoaffective disorder, or nonpsychotic bipolar disorder compared with the mental and behavioral capabilities of the young people who entered adulthood in good mental health.

The subjects who later developed schizophrenia had been significantly impaired on all intellectual aptitudes tested. These included verbal intelligence; verbal abstraction and categorization; mathematical reasoning, concentration, and concept manipulation; and nonverbal abstract reasoning and visual-spatial problem-solving abilities. In contrast, subjects who later developed schizoaffective disorder had been significantly impaired on only one of the intellectual proficiencies tested—nonverbal abstract reasoning and visual-spatial problem solving. Subjects who later developed bipolar disorder had not been significantly impaired on any of the intellectual skills that were assessed.

The subjects who later developed schizophrenia had been significantly impaired on reading ability and on reading comprehension, but not on writing ability. (In fact, their writing ability was significantly better than that of controls—a finding for which the investigators have no explanation, Davidson told Psychiatric News. ) In contrast, neither the subjects who eventually developed schizoaffective disorder nor those who eventually developed bipolar disorder had been significantly disabled in these language areas.

Regarding the behavioral competencies scrutinized—for example, the ability to function socially, organize one’s life, or function at work or school—subjects who later developed schizophrenia had been handicapped on all of them. In contrast, subjects who later developed schizoaffective disorder displayed deficits in all of these proficiencies but one, yet none of the differences reached statistical significance. Subjects who subsequently developed bipolar disorder performed similarly to controls on all behavioral abilities tested.

Taking all the results together, it appears that young people destined for bipolar disorder without psychosis do not differ from mentally healthy young people as far as intellectual, language, or behavioral capabilities are concerned; however, those adolescents who will eventually develop schizophrenia do. And those young people who eventually acquire schizoaffective disorder appear to lie in the middle—not quite at the same level as controls, but certainly better than those individuals who eventually develop schizophrenia.

Kenneth Davis, M.D., chair of psychiatry at Mount Sinai Hospital in New York City, is familiar with this study by Davidson and his team. As he told Psychiatric News, its “findings, coming from a population-based cohort, further support the nosologic distinction between schizophrenia and nonpsychotic bipolar disorder.”

The study, “A Population-Based Cohort Study of Premorbid Intellectual, Language, and Behavioral Functioning in Patients With Schizophrenia, Schizoaffective Disorder, and Nonpsychotic Bipolar Disorder,” is posted on the Web at http://ajp.psychiatryonline.org/cgi/content/full/159/12/2027?. ▪