According to the Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV), depressive mood can be seen in a number of psychiatric and medical disorders. Some physiologic effects of general medical conditions or medications can result in a diagnosis of mood disorders attributed to these causes. Involvement of manic symptoms can prompt a diagnosis of bipolar or cyclothymic disorder; and involvement of psychotic symptoms can result in a diagnosis of bipolar or schizoaffective disorder.
Individuals may also experience depressed moods that do not involve any of the above symptoms or conditions. In these situations, the available DSM-IV psychiatric diagnoses or conditions are major depressive disorder (MDD), dysthymic disorder, adjustment disorders (ie, with depressed mood or with mixed anxiety and depressed mood), bereavement, or depressive disorder not otherwise specified (NOS). According to the DSM-IV, the standard approach is to first determine whether the patient is experiencing a major depressive episode. The diagnosis of MDD requires a number of criteria, including the presence of 5 of 9 specified depressive symptoms for a period of at least 2 weeks. One of these symptoms should be either depressed mood or loss of interest or pleasure. When a major depressive episode is present, one considers the diagnosis of MDD.
When a major depressive episode is not present, one considers other diagnoses or conditions. The hallmark of dysthymic disorder is a depressed mood existing for a period of at least 2 years. If the depressed mood is linked to a stressor, one considers adjustment disorders; and if linked to a death, one considers bereavement. When clinically significant depressive symptoms do not meet any of the above criteria, one considers depressive disorder NOS.
But what happens when an individual has 2 to 4 depressive symptoms (including either depressed mood or loss of interest or pleasure) during a 2-week period, but has not had these symptoms for 2 years, and no particular event(s) can be linked to these depressive symptoms? Currently the individual would be diagnosed with depressive disorder NOS. But is there something more to this diagnosis severity than the catch-all category of depressive disorder NOS? The DSM-IV discusses what it calls "minor depression" (miD), which is characterized by the presence of 2 to 4 depressive symptoms during a 2-week period, and requires one of these symptoms to be either depressed mood or loss of interest or pleasure. A history of a variety of disorders, including MDD, excludes an individual from this category. At the time of publication, however, the authors of the DSM-IV concluded that there was insufficient information to include miD as a formal diagnosis.
This article reviews the prevalence, the depression continuum, and the impact of miD. It concludes with assessment and treatment considerations.
The Depression Continuum
The National Comorbidity Study conducted in the United States found that, over their lifetime, the estimated prevalence of miD is 10% for individuals ages 15-54 years. In analyses using the National Institute of Mental Health (NIMH) Epidemiologic Catchment Area (ECA) data in the United States, individuals older than 65 years had a 1-month point prevalence of 13% for miD. This was twice the prevalence for MDD among this age group. In literature reviews and meta-analyses, miD prevalence ranges from 2.2% to 23.4% in community settings[2-5] and from 4.5% to 17% in primary care and medical settings.[4,6] One caveat is that although these studies all examined miD prevalence, the measurement of miD differs slightly among the many available studies.
Minor Depression as Part of a Depressive Disorder Continuum
Many take the approach that a depression continuum exists, ranging from no depressive symptoms, to fewer depressive symptoms (miD), and finally to MDD. For example, in the National Comorbidity Study, individuals with miD (2-4 depressive symptoms; n = 810) were compared to those with MDD involving 5-6 symptoms (n = 664) and MDD involving 7-9 symptoms (n = 606). Individuals were asked whether depression interfered a lot with their lives and activities, and whether they saw a medical doctor about their depression, saw some other type of professional for their depression, or ever took medications more than once for their depression. For each of these 4 areas, the study found a consistent pattern of increasing percentages of individuals answering yes, with miD the smallest, followed by MDD involving 5-6 symptoms next, and MDD involving 7-9 symptoms having the greatest percentage answering yes. In an analysis including percentages for positive responses for any of these 4 questions, totals were miD, 42.0%; MDD 5-6, 49.7%; and MDD 7-9, 68.2%.
Using a similar approach, researchers in The Netherlands categorized individuals aged 18-64 years into 5 distinct groups relative to their depressive symptoms. These categories included no depression (n = 2838); 1 key depressive symptom (n = 198); miD (2-4 depressive symptoms; n = 429); MDD (5-6 symptoms; n = 97); and MDD (7-9 symptoms; n = 83). Individuals were compared on 8 different measures of functional disability (physical functioning, role functioning - physical, role functioning - psychological, vitality, mental health, social functioning, pain, and general health perception) as measured by the Short Form (SF)-36. They found a consistent pattern of increasing disability going from the no depression categories to miD and then the MDD categories.
A recent German study of 619 individuals ages 18 years or older from primary care settings revealed a similar pattern. These investigators used the Patient Health Questionnaire (PHQ-9) to assess depressive symptoms. They found a pattern of increasing number of days of impairment for items assessing total loss of daily activities, minor impairment, and missing work due to illness as the number of depressive symptoms rose, from nondepressive, to nonspecific depressive symptoms, to miD, to MDD.
A recent US study involving 1890 Puerto Rican adolescents did not show this continuum of increasing impairment depending on severity of depression. However, the study concluded that miD confers significant impairment similar to MDD and that those with miD use more health services than those with MDD. It may be that this continuum pattern occurs in adults.
Potential Impact of Minor Depression
Besides suffering functional disability, individuals with miD are likely over time to acquire the more severe and debilitating MDD. In a systematic review of miD, 2 studies showed that individuals with miD developed MDD. In the study with 1-year follow-up, 12.7% developed MDD; in the study with 6-year follow-up, 27% developed MDD. Furthermore, this review found 3 studies that showed that 6.7% to 59.5% of individuals with miD who were older than 50 years died within 2-13 years.
Two studies followed individuals for 15 years or more. The Zurich Cohort Study of Young Adults (aged 18 to 19 years at the beginning of the study)found that among those with subthreshold depression (n = 110) -- defined as those with either minor depression, depressive symptoms for at least 2 weeks, or recurrent brief depression -- 29% developed MDD. This was a higher rate of eventual MDD than for those with no subthreshold depression and suggests that subthreshold depression increases the risk for MDD. This subthreshold depression category is broader than the DSM-IV definition of miD and includes other depressive subtypes.
A recent US study used the Baltimore ECA data and focused specifically on those with miD. Subjects (N = 1634) included people ranging in age from 18-96 years at baseline. Among those with miD (n = 101), 18.8% developed MDD. The odds ratio that those with miD would develop MDD was 6.6. In analyses adjusting for demographic, psychosocial, and medical variables and the presence of anxiety, these odds ratios remained quite high, at 5.4.
Mental health clinicians typically conduct a comprehensive interview focusing on psychiatric, psychological, and/or psychosocial domains. During their assessment interview, it may be worthwhile to consider that those individuals with 2 to 4 depressive symptoms may have depressive symptomatology indicative of miD. It may be worth monitoring and considering these depressive symptoms as areas for extra consideration above and beyond the way one would assess and treat depressive disorder NOS.
Clinicians whose specialties are outside the mental health domain (eg, primary care) are often pressured to cover many topics in their limited-time interview. There are a few ways to incorporate miD screening and assessment into their practice with a minimum time commitment. One can administer questionnaires to patients while they are in the waiting room. For example, the paper Patient Health Questionnaire (PHQ-9) (English or Spanish language versions), and the computerized Center for Epidemiologic Studies of Depression Scale - Revised (CESD-R) both assess depressive symptoms and are available, free of charge, on the Internet. After completing the questionnaire, those whose depressive symptoms indicate significant distress should be followed up with specific questions by the clinician to determine presence of miD.
The single question, "Have you felt depressed or sad much of the time in the past year?" is a sensitive measure for depressive disorders and may be useful to routinely incorporate into clinical practice. In one study, asking this question was only a little less specific than the 20-item CES-D, a commonly used depression self-report questionnaire.
Although one can find a large amount of literature on miD, to this author's knowledge, no evidence-based guidelines or systematic reviews incorporate the literature published since 2002 on treatment of miD. What follows is a brief overview of the literature. This is not a systematic review, and the clinician is advised to carefully read the relevant studies before incorporating any particular treatments into clinical practice.
Oxman and Sungupta reviewed randomized controlled trials of treatment for minor depression and found no significant differences between the pharmacotherapy and control groups in 4 of 6 studies. Specifically, outcomes of patients receiving amitriptyline and isocarboxazid were not better than those of control groups. In one study, treatment with paroxetine produced better results. However, a second study did not find a benefit above that seen in controls. The authors concluded that antidepressants provide only a small benefit. In a review of 3 other studies, 2 studies reported improvements with paroxetine and minaprine, but not with amitriptyline. The authors concluded that these studies offer mixed support for antidepressant use.
Among empirical studies published since 2001, a series of treatment trials in individuals with minor depression in primary care found paroxetine to be beneficial for those with minor depression.[23-25] Fluoxetine, citalopram (in elderly men), and sertraline (among those with stroke) were also found to provide benefit.
In analyses of randomized controlled trials, one review reported that in 3 of 4 studies, patients in psychotherapy groups experienced better outcomes than those who were not in psychotherapy groups. Types of psychotherapy included cognitive-behavioral and interpersonal therapy. The authors concluded that psychotherapy provides small benefits, although they noted that these nonpharmacologic treatments produced larger effect sizes than the pharmacologic treatments in their review. Another analysis, which included 2 studies discussed in the previously mentioned review, found benefits for cognitive-behavioral therapy and problem-solving therapy. The authors concluded that there is mixed support for these treatments. Another review of some of the same studies concluded that evidence for the benefits of psychotherapy for miD is limited but promising.
Empirical studies published since 2001 found cognitive-behavioral therapy to be beneficial among the elderly; preliminary evidence for benefits of dynamic and supportive psychotherapy; and some benefits for group cognitive-behavioral therapy.
Recent studies have shown benefits of light therapy, dehydroepiandrosterone (DHEA), and St. John's wort for patients with miD.
More and more, the scientific literature is addressing miD. Studies have found that miD can be associated with functional impairment and can potentially result in MDD. Clinicians should incorporate brief assessment strategies for miD into their patient interviews. Minor depression is not so "minor," and clinicians may find it useful to monitor patients who have this symptom profile and provide treatment if indicated.