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IQ and global cognition

What is IQ and global cognition in bipolar disorder?

Intelligence quotient (IQ) is derived from standardised tests used to measure general cognitive functioning. IQ is most commonly measured using the Wechsler Adult Intelligence Scale (WAIS). The WAIS is designed to measure all aspects of cognitive functioning. It is divided into subtests measuring verbal comprehension and working memory and non-verbal perceptual organisation and processing speed. Other tests used to assess IQ include the Mini-Mental State Examination (MMSE), which assesses cognitive impairment; the National Adult Reading Test (NART), which assesses premorbid intelligence; the Wide Range Achievement Test (WRAT), which assesses both verbal and mathematic ability; and the Raven’s Progressive Matrices, which assesses general intelligence.

What is the evidence for IQ and global cognition in bipolar disorder?

Moderate to high quality evidence finds a small effect of poorer global cognition in people with bipolar disorder compared to controls without the disorder. This was found prior to the onset of the disorder when assessments were conducted retrospectively, but not prospectively. After illness onset, there was a medium-sized effect of poorer global cognition in people with bipolar disorder compared to controls, with no changes over time (3-7 years). The effect was smaller in people with first-episode patients than in chronic patients.

Moderate quality evidence finds a large impairment in global cognition in youth with bipolar disorder aged ~13 years who were matched to controls for age and IQ. There were no differences in global cognition in elderly people with bipolar disorder and controls matched for age and education.

High quality evidence finds a small effect of poorer global cognition in people with bipolar disorder and a history of psychotic symptoms compared to people with bipolar disorder with no history of psychotic symptoms. This effect was also found in people with bipolar I disorder compared to people with bipolar II disorder. There was also poorer global cognition in overweight people with bipolar disorder compared to normal weight people with bipolar disorder.

Moderate to high quality evidence finds no differences in IQ between first-degree relatives of people with bipolar disorder and controls. When the analysis included only relatives aged 10 to 25 years, high quality evidence shows a small effect of lower IQ in relatives. Moderate to high quality evidence finds a small to medium-sized effect of higher IQ in relatives of people with bipolar disorder than in relatives of people with schizophrenia.

October 2021

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Last updated at: 2:52 pm, 16th March 2022
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Tags:  General cognition

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