In the study were 111 elderly depressed subjects in their mid-70s, whose age of onset ranged from 40 to 60. They had no prior history of psychiatric disorder that could account for their disturbance. After administering neuropsychological tests for memory, frontal lobe function, depression and attention, the researchers performed a cluster analysis to look for subgroups and found three: those without neurocognitive impairment, those who had a frontal lobe presentation with a common memory impairment, and those with memory impairment alone.
The group least cognitively impaired had the youngest age of onset and the lowest level of disability. Remember, Van Gorp explained, that depression does not necessarily mean cognitive impairment.
The second group scored low on tasks of frontal lobe function and memory-the prototypal profile of depression. They had the latest age of onset and the greatest level of disability.
"These are the patients who come into your office and say, 'Help me.' The family comes in and says, 'I think she may be demented. She's not doing anything; she's not getting up off the couch.' These people have the greatest level of disability and this may be simply a reflection of their depression," Van Gorp said.
A third group, which had the highest levels of depression, but not the highest levels of disability, had memory impairment alone. Van Gorp plans on conducting a longitudinal study of this group and in the meantime hypothesizes that they are the ones who, over time, are at highest risk for irreversible dementia-ultimately Alzheimer's disease. "Could it not be," he queried, "that one reason it's hard for us as clinicians to differentiate between dementia and depression is because, in time, the depression in some older adults could be the first sign of what will emerge as a full-blown dementia syndrome?"
Three studies that have already looked at dementia and depression show that older adults with major depression are between two and three times more likely, over a three-year period, to develop Alzheimer' disease or another irreversible dementia. For this reason, follow-up is essential.
To Simplify and Summarize
Patients with cortical dementia (irreversible dementia) have normal speech volume but their language is impaired by a transcortical sensory aphasia-like syndrome, where they have severe anomia-the inability to name objects-and great circumlocution. Their comprehension, however, is relatively preserved. In terms of memory function, patients with cortical dementia have a defect in both recall and recognition; in subcortical dementia, recall is impaired while recognition is relatively intact. These patients cannot learn new information-every meeting with the patient is a new experience for the patient-and their cognition is impaired in many spheres. They often will have normal motor function and gait. They are cheerfully indifferent to their condition.
Patients with depression (reversible dementia) can be hypophonic but will have normal language. They have a forgetful memory pattern but can learn new information. They exhibit differential frontal lobe impairment, but not across all cognitive domains. They show psychomotor slowing and poor performance on effortful tasks. And they are pessimistic and brooding because they are painfully aware of their cognitive failures.
