Sant Joan de Deu SSM, Vilanova i la Geltrú, Barcelona, Spain
In their recent paper, Paterniti et al (2002) reported that depressive symptoms predict cognitive decline over a 4-year period. This is a well-designed and well-written study that replicates a previous finding from similarly well-designed studies. Negative findings on this question, however, are also common in the literature, including a report from the same French group a few years ago (Dufouil et al, 1996). I would like to point out some relevant issues overlooked by Paterniti et al.
First, I find it unfortunate that the paper cites few negative reports, with no mention in the discussion of the many longitudinal studies that have reported no association between depressive states and subsequent cognitive decline (Dufouil et al, 1996; Prince et al, 1996; Cervilla et al, 2000). It is particularly surprising that Paterniti et al quote the study by Chen et al (1999) as reporting that depressive symptoms are predictive of cognitive decline, when in fact they found that dementia predicted the onset of depressive symptoms but not the other way round.
Second, it is regrettable that Paterniti et al overlooked the only study to date addressing the very same question but for a considerably longer follow-up period (Cervilla et al, 2000). Longer follow-up periods could help to distinguish between psychopathology shared by depression and dementia (e.g. difficulties with memory and concentration, or apathy), as pointed out by a previous study by some co-authors of Paterniti's paper (Dufouil et al, 1996). Indeed it could be argued that if depressive symptoms have a real capacity to predict cognitive decline, the latter should be expected to become more apparent as the study's follow-up period lengthens. This, in fact, has not happened in our cohort (Prince et al, 1996; Cervilla et al, 2000) and I believe this adds potentially unique information to Paterniti et al's discussion.
Finally, it is also regrettable that Paterniti's group did not explore the repeatedly reported interaction with gender in considering whether depressive symptoms predict cognitive decline (Prince et al, 1996; Cervilla et al, 2000). Indeed, the latter studies have reported that if an association exists between depressive symptoms and cognitive decline, this seems to be the case in men only (Cervilla et al, 2000), or in men of above-median premorbid IQ (Prince et al, 1996).
REFERENCES
Cervilla, J., Prince, M, Joels, S., et al (2000) Does depression predict cognitive outcome 9 to 12 years later? Evidence from a prospective study of elderly hypertensives. Psychological Medicine, 30, 1017-1023.[CrossRef][Medline]
Chen, T., Ganguly, M., Mulsant, B., et al (1999) The temporal relationship between depressive symptoms and dementia. A community prospective study. Archives of General Psychiatry, 56, 251-266.
Dufouil, C., Fuhrer, R., Dartigues, J. F., et al (1996) Longitudinal analysis of the association between depressive symptomatology and cognitive deterioration. American Journal of Epidemiology, 144, 634-641.[Abstract]
Paterniti, S., Verdier-Taillefer, M. H., Dufouil, C., et
al (2002) Depressive symptoms and cognitive decline in
elderly people. Longitudinal study. British Journal of
Psychiatry, 181,
406-410.
Prince, M. J., Lewis, G., Bird, A., et al (1996) A longitudinal study of factors predicting change in cognitive test scores over time, in an older hypertensive population. Psychological Medicine, 26, 555-568.[Medline]
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