Mood disorder: Prognosis, Epidemiology, Comorbidity, and Differential Diagnosis

Epidemiology/ Prevalence

Depressive Disorders :

According to the DSM-5 (APA, 2013), the prevalence rate for major depression is approximately 7% within the United States. The prevalence rate for persistent depressive disorder is much lower, with a 0.5% rate among adults in the United States. There is a difference among demographics, with Individuals in the 18- to 29- year-old age bracket reporting the highest rates of depression than any other age group. Similarly, depression is approximately 1.5 to 3 times higher in females than males. The estimated lifetime prevalence for major depressive disorder in women is 21.3% compared to 12.7% in men (Nolen-Hoeksema, 2001).

Bipolar Disorders :

Compared to depression, the epidemiological studies on the rates of Bipolar Disorder suggest a significantly lower prevalence rate for both bipolar I and bipolar II. Within the two disorders, there is a very minimal difference in the prevalence rates with yearly rates reported as 0.6% and 0.8% in the United States for bipolar I and bipolar II, respectively (APA, 2013).

As for gender differences, there are no apparent differences in the frequency of men and women diagnosed with bipolar I; however, bipolar II appears to be more common in women, with approximately 80-90% of individuals with rapid-cycling episodes being women (Bauer & Pfenning, 2005). Women are also more likely to experience rapid cycling between manic/hypomanic episodes and depressive episodes.


Depressive Disorders :

As I’m sure it does not come as a surprise, studies exploring depression symptoms among the general population show a substantial pattern of comorbidity between depression and other mental disorders, particularly substance use disorders (Kessler, Berglund, et al., 2003). In fact, nearly three-fourths of participants with lifetime MDD in a large-scale research study also met criteria for at least one other DSM disorder (Kessler, Berglund, et al., 2003). Among those that are the most common are anxiety disorders, ADHD, and substance abuse.

Given the extent of comorbidity among individuals with MDD, researchers have tried to identify which disorder precipitated the other. The majority of the studies have identified most depression cases occur secondary to another mental health disorder meaning that the onset of depression is a direct result of the onset of another disorder (Gotlib & Hammen, 2009).

Bipolar Disorders :

Bipolar disorder also has a high comorbidity rate with other mental disorders, particularly anxiety disorders and any disruptive/impulse-control disorders such as ADHD and Conduct Disorder. Substance abuse disorders are also commonly seen in individuals with Bipolar Disorder. In fact, over half of those with Bipolar Disorder also meet diagnostic criteria for Substance Abuse Disorder, particularly alcohol abuse. The combination of Bipolar Disorder and Substance Abuse Disorder places individuals at a greater risk of suicide attempts (APA, 2013). While these comorbidities are high across both Bipolar I and Bipolar II, Bipolar II appears to have more comorbidities, with 60% of individuals meeting the criteria for three or more co-occurring mental disorders (APA, 2013).


  • The first step in the differential diagnosis of any mood disorder is to exclude a disorder with known organic cause, e.g. organic (especially drug-induced) mood disorders and dementia (differential diagnosis from depressive pseudodementia).
  • The second step is to rule out the possibility of acute and transient psychotic disorders, schizo-affective disorder, and schizophrenia.
  • The third step is to exclude the possibility of other non-organic psychoses such as delusional disorders.
  • The fourth step is to exclude the possibility of adjustment disorder with depressed mood, generalized anxiety disorder, normal grief reaction, and obsessive-compulsive disorder (with or without secondary depression).
  • In addition to the main diagnosis, it is also important to look for co-morbid medical (such as diabetes, hypertension) and/or psychiatric disorders.
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