PTSD and Depression: What is the link?

What is PTSD?

Post-traumatic stress disorder (PTSD) develops after someone experiences or witnesses an event that causes trauma, like war, a terrorist attack, or a natural disaster. PTSD symptoms fall into one of four categories, all of which must be present for a diagnosis:^[2]

• Intrusion symptoms, like recurrent and involuntary memories of the traumatic event.
• Avoidance symptoms, such as avoiding people, places, or things that remind you of the traumatic event.
• Cognition and mood symptoms, like a persistent negative state or feelings of detachment from others.
• Arousal and reactivity symptoms, such as angry outbursts or self-destructive behaviors.

These symptoms and the associated physiological responses (e.g., feeling on edge) must be present for a least a month following the traumatic event. Once symptoms occur, they can last for a long time, perhaps even years. PTSD can even become a chronic, lifelong disorder.

What is depression?

Major depressive disorder is a pervasive disorder characterized by psychological and physiological symptoms. Common symptoms of depression include:^[3]

• Feelings of helplessness or worthlessness
• Irritability
• Lack of interest in once-enjoyed activities
• Sleeping too much or too little
• Difficulty focusing

Like PTSD, depression can result from a traumatic experience and can be a chronic disorder. However, depression can also result from many other factors, including genetics, psychosocial circumstances, and environmental influences.

PTSD vs. Depression

As noted earlier, PTSD and depression have many similar symptoms. In fact, so many symptoms are shared by the two disorders that, in some cases, it can prove challenging to arrive at an accurate diagnosis.^[1] In that regard, it isn’t so much about PTSD vs. depression as it is about PTSD and depression.

PTSD vs Depression: Similarities

In examining the diagnostic criteria for PTSD and depression in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), we can see how similar these two mental health disorders are regarding symptomatology.^[2][4] Both can entail:

• Loss of interest or reduced participation in activities of significance
• Negative beliefs about oneself, self-blame, and feelings of worthlessness
• Sleep disturbances, such as insomnia
• Psychomotor agitation
• Irritable mood
• Difficulty concentrating
• Suicidal ideation

Moreover, both PTSD and depression can be chronic conditions. As mentioned above, PTSD typically lasts months or years, with some cases becoming a lifelong struggle. Major depressive episodes can last from six to twelve months, though these episodes can be persistent and reoccur over time.

PTSD vs Depression: Differences

Despite having many similarities, PTSD and depression also differ in several ways, including the most obvious - their etiology.

The DSM-5 notes that PTSD results from “exposure to actual or threatened death, serious injury, or sexual violence.”^[2]  This exposure can occur in many different ways, including experiencing a traumatic event directly, witnessing trauma occurring to others, or learning of a traumatic event that’s happened to a loved one.

Furthermore, PTSD might be caused by repeated exposure to details of a traumatic event. The DSM-5 offers the following example: police officers repeatedly exposed to elements of child abuse can develop PTSD.^[2]

Major depression, on the other hand, is caused by a myriad of factors, though biology is perhaps the most significant influence. People with major depressive disorder have an imbalance of neurotransmitters in the brain, primarily serotonin, norepinephrine, dopamine, and GABA.^[3]

What’s more, there appears to be a link between brain structures and major depression. For example, researchers have discovered that extreme stressors early in life can alter the makeup of the cerebral cortex, which can lead to the development of major depression as an adult.

Brain scans support this hypothesis - people with major depression have diminished brain metabolism, especially in the anterior areas on the left side. An increased hyperintensity in the subcortical regions of the brain is also evident in people with depression.^[3]

PTSD seems to have roots in a different part of the brain, though. Researchers have found that people with PTSD might have a smaller hippocampus than average and that other fear regions of the brain (e.g., amygdala, medial prefrontal cortex) are also involved.^[1]

However, the PTSD vs depression discussion goes deeper than their causes. Both disorders have distinct symptoms that the other does not.

For example, the DSM-5 notes that PTSD patients tend to have recurrent, involuntary, and distressing memories. Flashbacks and nightmares are also common.^[2] These events are not part of the diagnostic criteria for major depression.

As another example, the DSM-5 notes that major depressive disorder often involves a significant, unintentional change in weight and possible psychomotor retardation.^[4] Neither of these criteria is needed for a PTSD diagnosis.

From a purely diagnostic standpoint, PTSD is a much more complex disorder than major depression. The DSM-5 includes eight major criteria, many of which have many sub criteria to guide diagnosis. There are three specifying criteria as well.^[2]

The DSM-5 lists nine potential criteria for a major depressive episode, of which five must be present. Four additional criteria, mainly regarding other possible causes for the behavior in question, are also part of the diagnostic criteria for major depression.^[4]

PTSD and Depression: Comorbidity

Research shows that roughly 50% of people with PTSD also have a major depressive disorder.^[1] There are two schools of thought as to why comorbidity is so high.

First, as discussed earlier, PTSD and major depressive disorder share many common symptoms. On the one hand, it makes sense that one would occur with the other, given these similarities. But on the other hand, these similarities can make diagnosis difficult and might lead to an overdiagnosis of PTSD and depression as comorbid conditions.

A second explanation for the high comorbidity of these disorders is that PTSD and depression aren’t distinct. Instead, PTSD with depression might be a subtype of PTSD.^[1] An examination of risk factors seems to back this up:

• People with PTSD and depression exhibit more neurocognitive impairment than people with PTSD alone.
• People with higher levels of distress are more likely to develop PTSD and depression.
• People with PTSD and depression are more likely to exhibit suicidal ideation.
• The prognosis for someone with PTSD and depression is worse than someone with either condition on its own.

Moreover, people with negative affectivity (neuroticism) and low positive affectivity (extraversion) are more likely to develop PTSD and depression. In fact, studies show that high levels of neuroticism and low levels of extraversion are strongly associated with the development of PTSD and major depression within four years.^[1]

This same research also shows that neuroticism and extraversion are not associated with developing PTSD or major depression on their own. This indicates that the presentation of high neuroticism and low extraversion is a critical component of these disorders occurring together as PTSD depression.

Can PTSD cause depression?

PTSD is a risk factor for depression, just like depression is a risk factor for developing PTSD. For example, studies show that childhood trauma, which is the hallmark cause of PTSD, is also associated with the development of depression.^[5]

Likewise, research shows that an accumulation of trauma over a period of time, such as repeated physical assaults by one spouse on the other, is a risk factor for the development of depression.^[6] Again, since trauma is intertwined with PTSD, PTSD might develop first, with depression developing later.

While there is plentiful evidence that PTSD is a risk factor for depression, whether PTSD is a direct cause of depression is a little murky. More research is needed to clarify if that connection exists.

PTSD vs Depression: Treatment

PTSD and depression are both commonly treated with cognitive behavioral therapy (CBT). CBT is a form of talk therapy that explores your patterns of thinking and how to change those patterns for improved outcomes.

Another therapy - eye movement desensitization and reprocessing (EMDR) - is popular for treating PTSD depression. EMDR involves exposing a patient to their trauma (e.g., asking them to recall the details of the traumatic event) while simultaneously performing guided eye movements or experiencing other bilateral stimulation. This action helps reduce the emotionality and vividness of the trauma.

Likewise, PTSD and depression are often treated with antidepressant medications. SSRIs (selective serotonin reuptake inhibitors) like Zoloft and Paxil are particularly popular for both PTSD and depression.^[7]

There are some differences in treatment approaches between PTSD and depression, too. For example, group therapy is far more common for PTSD than major depression.^[8] Instead, most therapeutic treatments for depression occur in a one-on-one setting between the therapist and the patient.^[9]

Moreover, there seem to be more treatment options available for major depression than PTSD. For example, the American Psychological Association (APA) strongly recommends just four treatments, all of which are within the CBT realm:^[10]

• CBT
• Cognitive Processing Therapy (CPT)
• Cognitive Therapy
• Prolonged Exposure

However, the APA outlines no less than seven recommended therapy approaches for depression:^[11]

• Behavioral Therapy
• Cognitive Therapy
• CBT
• Interpersonal Psychotherapy (IPT)
• Mindfulness-Based Cognitive Therapy (MBCT)
• Psychodynamic Therapy
• Supportive Therapy

Despite these minor differences in treatment approaches, one thing is for sure: both PTSD and major depression respond well to treatment. The treatment modalities listed above aim to minimize symptoms, improve daily functioning, and provide patients with the resources they need to live effectively with their disorder.