Depressive symptoms increase the likelihood of cognitive impairment in elderly people with subclinical Alzheimer pathology.
Milwain EJ and Nagy Z;
Commented by , 22 Nov 2004
Aim of the study
To investigate whether the presence of depressive symptoms influences the clinical expression of Alzheimer pathology.
Method
89 consecutive subjects from a longitudinal research program with post-mortem evidence for Alzheimer's disease (AD). Cognition had been measured using the CAMCOG. The data on depression include answers from the subject, the informant and the impression of the interviewer.
Results
Depressive symptoms did not influence cognition in the early (entorhinal) stages of AD, whereas in the intermediate (limbic) stages, patients with depression had significantly worse cognitive performance than those who did not.
Professor Gauthier's comments
The authors conclude that depressive symptoms may contribute to the cognitive decline of AD, and that a multiple diagnosis of early AD and depression should be considered in elderly persons presenting with mild cognitive decline and depression.
These observations are congruent with a large body of data from epidemiological studies (for example ref. 1 and 2) demonstrating that depressive symptoms are common in early stages of AD and are a risk factor for AD. A group of investigators led by Jason T. Olin has put together provisional diagnostic criteria for depression in AD (ref. 3).
An excellent editorial by R Stewart in J Neurol Neurosurg Psychiatry (ref. 4) has highlighted the fact that most studies on "AD and depression" do not investigate depression but depressive symptoms, and that dysphoric symptoms predict a wide variety of adverse symptoms, but are rarely measured in any detail.
There should thus be a concerted effort to use a well structured measurement scale such as the NeuroPsychiatric Inventory (NPI), possibly supplemented by depression-specific scales, in prospective observational or therapeutic studies in healthy aging as well as mild cognitively impaired (MCI) populations.
An analysis of the baseline characteristics of non-depressed subjects enrolled in an amnestic MCI study has demonstrated a number of behavioral symptoms using the NPI (ref. 5), and it is reasonable to predict that those with behavioral symptoms will convert to AD at a faster rate than subjects with none.
References
1. Berger et al. The occurrence of depressive symptoms in the preclinical phase of AD: a population-based study. Neurology 1999; 53: 1998-2002
2. Green et al. Depression as a risk factor for Alzheimer disease: the MIRAGE Study. Arch Neurol 2003; 60: 753-759
3. Olin et al. Provisional diagnostic criteria for depression of Alzheimer disease. Am J Geriatr Psychiatry 2002; 10: 125-128, updated in Expert Rev Neurotherapeutics 2003; 3: 99-106
4. Stewart J. Depressive symptoms and cognitive decline - disentangling the effect of affect. Neurol Neurosurg Psychiatry 2004; 75 (1): 5
5. Feldman et al. Behavioral symptoms in mild cognitive impairment. Neurology 2004; 62 (7): 1199-1201