Medical Illness

The first important step in diagnosing depressive disorders is to have the patient get a complete physical. Depression commonly co-occurs with other mental disorders (e.g., anxiety disorders) and physical disorders (King-Kallimanis, Gum, & Kohn, 2009), which can further exacerbate distress and disability, and can challenge treatment efforts. Because many medical illnesses are related to the onset of a depressive episode, at times treating both the illness and the depression is a more efficient way to effect symptom change (Gupta, Bahadur, Gupta, & Bhugra, 2006; Katon, 2003; Simon, Von Korff, & Lin, 2005; Stover, Fenton, Rosenfeld, & Insel, 2003; Trivedi, Clayton, & Frank, 2007). For example, in endocrinological disorders like hyperthyroidism and hypothyroidism, one of the diagnostic signs is a change in affect and mood. People who are treated for these disorders experience radical changes in mood. Moreover, people with chronic illnesses like diabetes mellitus have high rates of depressive symptoms (de Groot, Jacobson, Samson, & Welch, 1999; Renn, Steers, Jay, & Feliciano, 2013), but not necessarily higher rates of MDD or persistent depressive disorder (Fisher, Glasgow, & Strycker, 2010; Fisher, Mullan, et al., 2010).

Acute medical illnesses such as stroke (Sagen et al., 2010), Parkinson’s disease (Caap-Ahlgren & Dehlin, 2001), pancreatic cancer (Jia et al., 2010; Mayr & Schmid, 2010), coronary heart disease (Kubzansky & Kawachi, 2000), and myocardial infarction (Martens, Hoen, Mittelhaeuser, de Jonge, & Denollet, 2010) are also associated with depressive symptoms. Neurological findings suggest that cerebrovascular disease (particularly ischemic small-vessel disease) may be related to the onset of late-life depression (Rapp et al., 2005). Although it is unclear whether these illnesses directly cause depression or the depression is the result of the life changes brought on by the illness, recovery from these diseases (when possible) will help alleviate depressive symptoms.

Drug and Alcohol Abuse

The next step in establishing a diagnosis is to determine to what extent the person drinks alcohol or uses drugs. Often substance abuse or dependence disorders are strongly associated with depressive symptoms (Gunnarsdottir et al., 2000; Merikangas & Avenevoli, 2000; Ostacher, 2007). Scientists have debated whether depressive symptoms are a consequence of substance abuse and the problems related to this disorder, or whether the substance use is a means of self-medicating depressive symptoms. The psychiatric and substance abuse fields are slowly moving toward the co-management of depression and substance abuse, and while abstaining from substances does often clarify the diagnostic picture, it is often very unlikely that someone who is abusing substances and has depression will be able to abstain without treatment. Therefore, when these two conditions do present together, clinicians generally ascribe a dual diagnosis and attempt to untangle which disorder was apparent first through gathering a thorough diagnostic history.

In determining the best course of action regarding treatment, it is crucial to get a list of all medications (both prescribed and over-the-counter) the person uses, given that the side effects of many medications can cause or contribute to the depressive symptoms observed. This is particularly true with older adults, who are more vulnerable to the side effects of medication. For example, in a review of late-life depression, Dick, Gallagher-Thompson, and Thompson (1996) note that some medications, such as antihistamines, antihypertensives, some antiparkinsonian drugs, and some pain medications, commonly cause symptoms of depression. In addition, diuretics, synthetic hormones, and benzodiazepines have also been noted to contribute to depressive symptomatology (Cooper, Peters, & Andrews, 1998). The higher the number of drugs the person takes, the higher the risk for medication side effects and drug–drug interactions—a situation that emphasizes the need for good assessment of drug regimens.

Grief and Bereavement

Grief over the loss of a special person or the presence of a major life stress or change can also complicate attempts to diagnose depressive disorders. Although bereavement may produce a grief response that mimics symptoms of depression, it was previously an exclusion for a diagnosis of MDE or a mood disorder (bereavement in the DSM-IV-TR was assigned a V-Code falling under Additional Conditions that may be a Focus of Clinical Attention). This exclusion was originally intended to prevent misdiagnosing “normal” grief as depression (Maj, 2008). Therefore, the removal of the bereavement exclusion has created controversies in the field; some clinicians criticized that bereavement was the only psychosocial stressor to exclude an individual from an MDE diagnosis (Wakefield et al., 2007), whereas others conceptualize grief as a normal reaction to loss and are loathe to pathologize it.

The DSM-5 recognizes that a significant psychosocial stressor, such as a loss of a loved one, can trigger a mood disorder. Because of the overlap between “normal” grieving and depression, careful consideration is given to delineate what is a normal or appropriate response, with consideration given to the person’s history and cultural norms. In making this distinction, clinicians must use their judgment to decide whether symptoms (e.g., sadness, weight loss) are appropriate for the loss or whether the symptoms more resemble those associated with a depressive episode. For example, grieving is typically classified by feelings of emptiness and loss, whereas depression is associated with a persistent sadness and an inability to experience pleasure or happiness. Also, grief is often experienced in waves of dysphoria, longing, and/or yearning, typically brought on by reminders of the deceased. These pangs of grief might also include positive emotions associated with these memories. In contrast, the unhappiness of depression is persistent and pervasive, and not associated with specific thoughts or memories.

Although it is possible that those with uncomplicated bereavement or adjustment disorder can develop a depressive disorder, little is known about the extent to which grief can develop into depression (Boelen, van de Schoot, van den Hout, de Keijser, & van den Bout, 2010; Wellen, 2010). However, when bereavement and a depressive episode co-occur, the individual often experiences more severe functional impairment and a worse prognosis (Shear et al., 2011; Zisook, Simon, et al., 2010) than bereavement not accompanied by depression. Individuals with other vulnerabilities to depression (e.g., poor social support, trauma history, increased stressors) may be more apt to experience a major depressive episode with bereavement (Ellifritt, Nelson, & Walsh, 2003; Shear et al., 2011).

Depression Due to Other Psychiatric Disorders

Adults with other psychiatric disorders can have co-occurring depressive symptoms, and thus establishing a differential rule-out for these other disorders is often important. For instance, people with anxiety disorders, particularly generalized anxiety disorder, report feelings of sadness and hopelessness (Hopko et al., 2000). Co-occurring mood and anxiety disorders are also more commonly reported in middle-aged and older women than men (Byers et al, 2009). When under stress, people with personality disorders will also report significant symptoms of depression (Petersen et al., 2002). In fact, they can become quite acutely depressed. Specifically, depressive episodes are most prevalent with avoidant, borderline, and obsessive-compulsive personality disorders (Rossi et al., 2001). Furthermore, personality disorders have an association with a longer remission onset from a depressive episode (O’Leary & Costello, 2001). Finally, depression is common in prodromal phases of schizophrenia and is a recurrent feature in bipolar disorder.

Late-Life Depression

Depression, although not a natural consequence of aging, is one of the most common mental health disorders that older adults experience. Prevalence rates differ depending on the population surveyed and the settings observed (see Epidemiology section). Older adults present differently than younger populations in that they are less likely to report feeling sad or depressed (Fiske, Wetherall, & Gatz, 2009) or symptoms of guilt (Gallagher et al., 2010) and may report more anhedonia, memory problems (in the absence of dementia), and somatic symptoms such as fatigue, decreased appetite, and muscle pain (Kim, Shin, Yoon, & Stewart, 2002). In addition, because older adults are more likely to have chronic illnesses, the presence of physical illnesses as well as the side effects of medications taken to treat these conditions can overshadow or worsen symptoms of depression (Areán & Reynolds, 2005), which can further complicate diagnosis. In older populations, depression is also associated with increased mortality and health service usage. This association highlights the importance of early recognition, differential diagnosis, and treatment of this disabling illness.

Community Samples

Depressive disorders are serious and relatively common. Based on DSM-IV-TR criteria, the lifetime prevalence, or the number of persons who have ever experienced any type of mood disorder, is 20.8% (Kessler et al., 2005). The NCS-R (Kessler et al., 2005) found a lifetime prevalence for an episode of major depression to be 16.6% in a community-dwelling sample, with a 12-month prevalence of 6.6% (Kessler et al., 2003). Previous estimates of MDE were as low as 5.8% (Regier, 1988) using DSM-III-R diagnostic criteria. These studies also indicate that in a given 6-month period, approximately 3% to 9% of the general population will experience an episode of major depression (Kessler, McGonagle, Zhao, et al., 1994; Regier, 1988). The lifetime prevalence for dysthymic disorder is lower than the rates for MDD. According to the NCS and the NCS-R (Kilzieh, Rastam, Ward, & Maziak, 2010), between 2.5% and 6% of the general population has had a period of Persistent Depressive Disorder, pure dysthymic syndrome in their lifetimes. No nationally representative prevalence data are yet available for the new DSM-5 diagnostic label of persistent depressive disorder.

Prevalence by Gender

The ECA and the NCS show differential prevalence by gender. In the ECA studies, lifetime prevalence of affective disorders for adult women average 6.6%, whereas in the NCS, prevalence is significantly higher at 21.3% (Kessler, McGonagle, Nelson, et al., 1994; Regier, 1988). The lifetime prevalence for men was 8.2% in the ECA and 12.7% in the NCS. Although prevalence for depression varied between these two studies, a consistent theme emerges: More women than men report having depressive episodes. The most recent nationally representative prevalence data from the NCS-R found that women are at a 1.5-fold increased risk (compared to their male counterparts) of developing a mood disorder over their lifetime, and a 1.7-fold increased risk of developing MDD specifically (Kessler et al., 2003; Kessler et al., 2005). This difference between men and women has been found repeatedly throughout the world and thus appears to be accurate reflections of true differences in the prevalence of the disorder between men and women (Kessler, 2003). Although the reasons for these differences are relatively unknown, some speculate that sex differences in biological makeup, differences in cognitive and behavioral patterns of mood control (Nolen-Hoeksema, 2000), and social influences, including differential expectations for the two genders, account for the difference in prevalence (Kilzieh et al., 2010).

Prevalence by Age Cohort

The prevalence of depressive disorders in the United States varies by age, with the NCS-R reporting a peak in 12-month prevalence of MDD during the ages 18–29 (Kessler et al., 2003). Prevalence in this age group is threefold higher than the prevalence in individuals 60 years or older; rates drop to a 1.8-fold and 1.2-fold increased risk for adults aged 30–44 and 45–59, respectively (Kessler et al. 2003). The NCS-R included individuals over the age of 60 and up to the age of 75, which is an improvement over the demographics in the previous ECA and NCS samples (Kessler & Merikangas, 2004). As Burke, Burke, Rae, and Regier (1991) first pointed out, rates for all psychiatric disorders are increasing with each decade, indicating that disorders like depression may be influenced by cohort effects, including willingness to self-disclose symptoms and differences in measures utilized (Richards, 2011). However, the information presented by the NCS-R on the differential prevalence rates of depression between younger and older people is limited and does not include our fastest-growing segment of the population, the “oldest-old” (those age 85 and older). With the preceding caveat in mind, it is important to highlight what is known about the prevalence of depression in older adults.

The prevalence of depression among older adult populations is one of the highest of any mental disorder (Baldwin, 2000; Kessler et al., 2005). The NCS-R reports lifetime prevalence of mood disorders for individuals over the age of 60 to be 11.9%, with the majority of these cases accounted for with the diagnosis of MDD (10.6%; Kessler et al., 2005). However, it is important to keep in mind that the prevalence of depression varies substantially by population studied (e.g., NCS-R study did not include institutionalized older adults), and is affected by other sociodemographic variables such as gender, socioeconomic status, and race/ethnicity. Also, the difficulties in detecting depression in older adults (see Late-Life Depression) make this a difficult population from which to obtain precise epidemiological data.

Prevalence in Minorities

Rates of depression also vary by ethnic group. According to the NCS data, African Americans have rates of depression similar to those of the Caucasian population. Approximately 3.1% of African Americans have had an MDD episode, and 3.2% have had persistent depressive disorder, pure dysthymic syndrome (Jackson-Triche et al., 2000). However, Asian Americans have the lowest rates, with only 0.8% reporting that they had experienced an MDE and 0.8% experiencing persistent depressive disorder, pure dysthymic syndrome (Jackson-Triche et al., 2000). Hispanics/Latinos were found to have an interesting presentation of prevalence that depended on immigration status. According to Alderete, Vega, Kolody, and Aguilar-Gaxiola (1999), Hispanics/Latinos who recently emigrated from Latin America were less likely to have depression than Hispanics/Latinos who were born and raised in the United States. Hispanics/Latinos who were U.S.-born had rates of depression much like the rates of Caucasians (3.5% for MDD and 5% for persistent depressive disorder, pure dysthymic syndrome), whereas immigrants reported only half the prevalence of U.S.-born Hispanics. Although unconfirmed empirically, Vega, Kolody, Valle, and Hough (1986) believe that lower rates in immigrants result from a heartiness factor; those who are able to withstand the stress related to immigration are more likely to cope with stress related to depression.

There are two relatively new studies aimed at capturing higher numbers of minorities in epidemiological research: First, the National Latino and Asian American Study (NLAAS), is a household survey that includes nationally represented samples of adults from various ethnic groups (i.e., eight different ethnic and subethnic groups including Latinos, Asian-Americans, African Americans, and non-Latino Whites) (Alegría et al., 2004). Second, National Survey of American Life (NSAL), a household survey of community dwelling African-American and Black adults (Caribbean). In a recent study, the data from the NLAAS, the NCS-R, and the NSAL were statistically treated and combined into a single dataset (n = 8762). This study found the 12-month prevalence rates of depressive disorders was higher than that found in earlier epidemiological studies; 5.4% for Asians, 10.8% for Latinos, and 8% for African-Americans compared to 11.2% for non-Latino Whites (Alegría et al., 2008). This study also confirmed that of those with depressive disorders, an alarming number did not receive any kind of mental health treatment or received inadequate treatment (Alegría et al., 2008), highlighting the need for better assessment and treatment of depression for diverse groups.

Prevalence in Special Settings

Prevalence of depression in certain settings is greater than what has been found in the general community. For instance, people who have depression are more likely to seek help in primary care settings (Wagner et al., 2000). Estimates vary, but most studies indicate that what used to be referred to as minor depression is the most common depressive disorder, with as many as 25% of patients meeting diagnostic criteria (Wagner et al., 2000). Although the prevalence of depressive disorders may be high, recurrence is lower in these settings than in the community. According to van Weel-Baumgarten, Schers, van den Bosch, van den Hoogen, and Zitma (2000), patients treated in primary care medicine are less likely to suffer a relapse or remission than those treated in psychiatric settings. However, psychiatry tends to manage more severely depressed patients, and thus this finding is likely an artifact of the populations served in each setting.

Another setting with high rates for depression is long-term care. Approximately 32% of people living in assisted living facilities experience MDD (Waraich et al., 2004), with new episodes occurring in 31.6% of patients within the first 12 months of admittance (Hoover et al., 2010). The causes for higher prevalence of depressive disorders in nursing home facilities may vary but most likely include loss of functional independence, loss of familiar surroundings, decreased access to pleasant activities or loved ones, and comorbid physical illnesses. Given the impact that depressive disorders have on rehabilitation, the high rate of these disorders in these settings is cause for concern and argues for more vigilant and proactive treatment of depression in long-term care.