Research reportA tune in “a minor” can “b major”: A review of epidemiology, illness course, and public health implications of subthreshold depression in older adults
Introduction
With the introduction of the DSM-III, psychiatry increased reliability of its diagnoses, including major depressive disorder (MDD) (Judd et al., 1994). The establishment of boundaries at which the frequency, duration, or severity of symptoms crossed a “threshold” sufficient to be labeled psychopathology was not simple, however. When possible, thresholds were based on empirical data, but otherwise, non-empirical “expert opinion” was involved in separating the “ill” from the “well.” With emphasis on dimensional aspects of psychopathology in development of the upcoming DSM-V, now may be an opportune time to explore the merits of better defining various continua of disorders such as depression. Subthreshold depression (SubD) has sometimes been divided into distinct categories (e.g. minor depression [MinD], recurrent brief depression, and subsyndromal depression [SSD]), but at other times studied as a single entity. Based on the diagnostic criteria used in studies, overlap among these constructs is common. We exclude dysthymia (DYS) as a type of SubD because it has well-defined DSM-IV-TR (First et al., 2002) criteria, and most SubD studies do not include it.
In 1992, Wells et al. (1989) reported that depressive symptoms not qualifying as MDD were associated with more social disability than many medical illnesses. Soon thereafter, Judd et al. (1994), in analyses from the Epidemiological Catchment Area (ECA) study (1982), reported a one-month prevalence of SSD in the general adult population of 11.8%. DSM-IV later listed criteria for MinD among its research diagnostic criteria in the section on Depression Not Otherwise Specified. These were similar to those for MDD except requiring only 2–4 symptoms and no prior history of MDD; however, subsequent research has shown that DSM-defined MinD misses a substantial number of people who suffer morbidity from other variants of SubD. For instance, Judd et al. noted that among the SubD subjects in the ECA study, less than a third met criteria for MinD because neither depressed mood nor anhedonia (MDD Criterion A symptoms) were present (Judd et al., 1994). The investigators found virtually no differences between SubD subjects with versus without Criterion A symptoms. Angst et al. (1990) proposed another variant of SubD—recurrent brief depression, in which the only reason for failing to meet MDD criteria was that symptoms did not persist uninterrupted for two consecutive weeks.
Despite variable definitions and criteria, “non-major” depressions consistently exact major consequences on affected individuals (e.g. increased disability, poorer quality of life) and on society (e.g. increased healthcare costs) (Broadhead et al., 1990, Hybels et al., 2001, Sptizer et al., 1995, Xavier et al., 2002, Koenig, 1998). The concept of SubD resonated strongly in geriatric psychiatry (Jeste et al., 1999, Jeste et al., 2005), along with a speculation that MDD prevalence among older adults was inaccurate in the ECA study because of diagnostic ascertainment procedures (Judd and Akiskal, 2002). Re-analyzing the ECA data, Judd and Kunovac (1998) found that among adults ≥ 65 years old, SubD (MinD + SSD) prevalence was 31.1%, versus 6.3% for MDD—a fivefold difference.
Given the preponderance of SubD compared to MDD in older adults and the increasing research on late-life SubD, we believe an updated review of SubD in older adults is warranted. Specifically, we focus on the following aspects of late-life SubD, for which we know of no recently published comprehensive review: epidemiology, longitudinal time course, risk factors and public health consequences.
Section snippets
Methods
We searched PubMed (1980–January 2010) using combinations of the following search terms: Group (A) subsyndromal depression, subthreshold depression, and minor depression with Group (B) elderly, geriatric, late-life, and older adult. Additional articles were identified via manual review of references in articles from database searches. We extracted data from articles in English conducted among older adults (age ≥ 55 years) that focused on any depressive condition with proposed criteria other than
Results
We identified 153 unique, potentially relevant articles by database searches (Fig. 1). Although we used search terms geriatric, older adult, and late life for thoroughness, these terms yielded no articles other than those discovered with the search term elderly, hence the omission of these other search terms in Fig. 1. An additional 28 studies of interest were identified via manual review of database-generated articles.
Discussion
The evidence reviewed above strongly suggests that late-life SubD, howsoever defined, is prevalent, worsens quality of life and health of older adults, and impacts healthcare systems via increased service utilization and cost expenditure. Epidemiological research on late-life SubD demonstrated a pattern observed in late-life MDD: increasing prevalence moving from community to PC to LTC settings (community [10%], PC [25%], medical inpatients [30%+], LTC [c. 45–50%]). SubD was consistently at
Role of funding source
This work was supported in part by grants from the National Institute on Mental Health (P30 MH080002), the National Institute on Aging (T35 AG26757), and The US Health Resources and Services Administration (Geriatric Academic Career Award), the UCSD Sam and Rose Stein Institute for Research on Aging, the John A. Hartford Center of Excellence in Geriatric Psychiatry, and the Department of Veterans Affairs.
Conflict of interest
Dr. Lavretsky has a research grant from the Forest research Institute.
AstraZeneca, Bristol-Myers Squibb, Eli Lilly, and Janssen donate medication to Dr. Jeste's NIMH-funded research grant, “Metabolic Effects of Newer Antipsychotics in Older Pts.”
No other authors have any conflicts of interest.
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