Subsyndromal Depression in Very Old Persons

Abstract

Background: Subsyndromal depression (SSD) or subthreshold depression is a common affective condition that can be described as depressiveness below the threshold of what is called a syndromal or a major depressive episode. The point prevalence for SSD has been reported to be about 10% in the community, or about two or three times higher than the prevalence for syndromal depression. In elderly persons, SSD compared to non-depression (ND) is associated with impaired activities of daily living (ADL), lower cognitive function, lower self-perceived health, worse psychiatric outcomes and higher mortality. However, most studies on SSD in elderly persons have been done in the young old age group (age 60-80 years), while few studies have investigated SSD in very old persons (age 80+). As many aspects (e.g. multimorbidity, frailty, functional decline and social dependence) increase between the young old and the very old ages, there is a need for more knowledge about SSD in the very old. The overall aim of this doctoral thesis was to describe SSD, or the unclear area between syndromal depression and normal aging, in very old persons. Method: Paper 1 was based on qualitative interviews (n=27), while papers 2-4 were based largely on data from a prospective observational cohort study "Elderly in Linköping Screening Assessment" (ELSA85), with a population-based design following the participants from the age of 85 in three waves of follow-up. The 15-item Geriatric Depression Scale (GDS-15) was used for measuring depressiveness and to define SSD in the studies. Results: The analysis of the qualitative interviews (paper 1) resulted in four themes (life curve and the body go down, to manage on one's own, to keep up with life, and taking one day at a time), giving a comprehensive picture of SSD in very old age. In a comparison among SSD, ND and syndromal depression, SSD differed qualitatively from syndromal depression, but not clearly from ND. A cross-sectional analysis of data from baseline (paper 2) identified factors associated with SSD in very old persons, and according to analyses with multiple logistic and linear regressions, four domains (sociodemographic factors, declining physical functioning, neuropsychiatric factors, and existential factors) were significantly associated with SSD. A five-year longitudinal follow-up (paper 3) showed that direct healthcare costs per month of survival for persons with SSD exceeded those of persons with ND by a ratio of 1.45 (€634 vs €436), a difference that was significant even after controlling for somatic multimorbidity. An eight-year longitudinal follow-up (paper 4) showed that morbidity was elevated for persons with SSD compared to ND regarding basic ADL, I-ADL, loneliness, self-perceived health and depressiveness, whereas cognitive speed, executive functions and global cognitive function were not significantly lower when adjusting for covariates. Contrary to our hypotheses, mortality over