Errors of omission and commission in distinguishing patients with dementia of the alzheimer-type and patients with the dementia syndrome of depression




Amanullah, Soraya Lotus

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Dementia is characterized by a progressive decline in intellectual, memory and other cognitive functions. Alzheimer's disease (DAT) is the most prevalent cause of dementia in later life. Memory impairment may be the first symptom to herald the onset of the disease. The dementia syndrome of depression (DEP) may also be associated with a memory impairment which may masquerade as dementia in the elderly. Thus both types of patients may present with memory problems; DAT patients may also experience concomitant depression, and the distinction between DAT and DEP patients may be a difficult one. The current criteria for the diagnosis of DAT are generally exclusionary, that is, other possible causes of the dementia need to be ruled out before making the diagnosis. Therefore, the identification of a neurobehavioral marker for DAT could increase diagnostic accuracy by reducing the overall error rate. Alterations in neurotransmitter systems have been found in neurologic and psychiatric conditions. Decreased cholinergic functioning has been associated with DAT while disruption of the noradrenergic system has been postulated in depression. Recurrent perseverations, the inappropriate repetition of a previous stimulus or response into a current response, have been associated with cholinergic system dysfunction (Fuld, 1982). Continuous perseverations, the inappropriate repetition of aspects of the current response, have been associated with noradrenergic functioning (Sandson & Albert, 1987). Thus, a qualitative scoring of memory tasks for the presence and types of perseverative errors may serve to increase diagnostic accuracy. In particular, we hypothesized that scoring errors of commission as well as errors of omission could be used to classify subjects into diagnostic groups. Additionally, we hypothesized that the DAT group would make a higher proportion of recurrent perseverations than the DEP group, while the DEP group would make a higher proportion of continuous perseverations. Data from one verbal and one visual subtest of the Wechsler Memory Scale (WMS, Wechsler, 1945) from 49 DAT patients and 39 DEP patients were rescored for the presence of both errors of omission and errors of commission. These error scores were used in a discriminant function analysis with 85 percent correct classification overall. Commission errors were also scored for the type of error, i.e. recurrent or continuous. Proportion scores were derived for the number of each type of perseverative error to the total number of perseverative errors. A multivariate analysis of variance on the proportion scores demonstrated that the DAT group produced a higher proportion of recurrent perseverative errors than did the DEP group. Further, the DEP group produced a higher proportion of continuous perseverations than did the DAT group. Results were discussed in relation to possible underlying mechanisms.



Dementia, Patients, Alzheimer's disease, Senile dementia