Almost 20% of the depressed patients scored in the impaired range on tasks of scanning and visual motor tracking relative to normal controls. Visual-spatial abilities showed a high degree of variability. Many clinicians have been taught that depressed patients could draw but that demented patients could not; that a patient who could not copy a complex figure had dementia and not depression. "That has not been borne out in the literature," Van Gorp said. "In fact, 15% of the depressed patients scored in the impaired range relative to the normals."
In memory recall tests, 15.5% of the depressed individuals scored in the impaired range, and their rates of forgetfulness were twice as high as control subjects.
Mental inflexibility proved to be a key factor. If there's one cognitive defect that is characteristic of people with major depression, said Van Gorp, it is the disturbance of mental flexibility.
Half of all depressed subjects scored in the impaired range relative to normal controls, showing great difficulty in tasks of mental flexibility, perseveration, set shifting and response inhibition. This finding was consistent with the findings of imaging studies, which revealed altered metabolic or blood-flow activity in the frontal lobes, particularly the left, of patients with syndromal depression.
In drawing conclusions from these various studies about depression, Van Gorp said, "There's little effect, surprisingly-and this goes contrary to our clinical intuition-on measures of attention and concentration. We see the largest effect on tasks of mental flexibility and frontal lobe functions, and an intermediate effect on many other cognitive tasks, such as memory. But the results do indicate clear deficits in a subgroup of depressed individuals, ranging from about 10% to 15% of depressed individuals."
What if, even after testing, it looks like a patient has all three: depression, dementia and normal aging?
"In cases where there is no clear-cut differential between a subcortical dementia, let's say, and depression affecting cognition, the rule is: treat and reevaluate," he said.
To see whether all elderly, depressed patients looked alike on neuropsychological testing or whether there were identifiable subgroups which might help clinicians recognize patterns, Van Gorp and colleagues conducted a study.
