Persistent depressive disorder (PDD) and major depressive disorder (MDD) are two forms of depression. Both conditions can affect a person’s daily life.
PDD, formerly called dysthymic disorder, affects 1.5% of adults in the United States. Females are more likely to have PDD than males.
MDD is one of the most common mental health disorders in the U.S., affecting 7.1% of adults in the country. It is also more likely to develop in females than males.
A key difference involves the duration of symptoms. For a doctor to diagnose PDD in an adult, symptoms must have lasted for at least 2 years. Adults with MDD, meanwhile, experience what are called major depressive episodes that are separated by at least 2 months.
Below, learn more about the differences between major and persistent depressive disorders. We describe their symptoms, causes, treatment, and more.
PDD and MDD have very similar symptoms. It is possible for a person to have symptoms of both disorders at the same time.
MDD symptoms
There are many symptoms of MDD, and not all of them have to be present at the same time for a doctor to diagnose the issue.
The symptoms of MDD are:
- having a depressed mood that lasts for most of the day
- having less interest or pleasure in most or all activities
- experiencing fatigue
- feeling worthless or guilty
- having difficulty concentrating and making decisions
- unintentionally losing or gaining a significant amount of weight
- having trouble sleeping — insomnia — or sleeping too much
- experiencing a type of restlessness called psychomotor agitation or finding it difficult to think, speak, and do other everyday things, called psychomotor impairment
- having frequent thoughts of death
PDD symptoms
The symptoms of PDD somewhat overlap with those of MDD.
As with MDD, not every PDD symptom needs to be present at the same time for a person to receive a diagnosis.
PDD symptoms include:
- feeling depressed or irritable
- having a poor appetite or overeating
- having insomnia or sleeping too much
- experiencing fatigue or low energy
- having low self-esteem
- having trouble concentrating or making decisions
- having feelings of hopelessness
While some causes of MDD and PDD may be similar, there are some crucial differences.
MDD causes
Mood disorders have genetic and external causes. In the case of MDD, scientists do not yet know how these factors interact, and they believe that each symptom of MDD may have different causes.
However, researchers believe that a part of the brain called the hippocampus plays a large part in MDD — in a person with MDD, the hippocampus is smaller than that of a person without the disorder.
The hippocampus helps with making memories, adapting to stressful situations, and processing emotions. A reduction in the size of this part of the brain can affect its ability to function.
MDD also reduces the amount of gray matter in the brain. Gray matter is involved in numerous processes, including speech, decision making, and self-control.
The neurotransmitters serotonin, dopamine, and norepinephrine travel through gray matter. When MDD reduces the amount of gray matter, this disturbs the passage of these neurotransmitters, leading to the symptoms of the disorder.
Factors that increase the chances of developing MDD include:
- having had depressive episodes
- experiencing a stressful life event
- having a family history of MDD
- having chronic medical conditions
- having dementia
- having anxiety
- engaging in substance abuse
PDD causes
Research into the causes of PDD is ongoing, but scientists believe that the disruption of the neurotransmitters serotonin, epinephrine, norepinephrine, and glutamate plays a role.
Researchers have also found that certain parts of the brain, such as the orbitofrontal cortex and the hippocampus, are smaller in people who have PDD than those who do not.
Other causes of PDD are genetic, environmental, and psychological. Some of these include:
The diagnostic processes for PDD and MDD are similar.
MDD diagnosis
Doctors, including psychiatrists, use the symptoms of MDD to diagnose it.
For a doctor to recognize MDD, a person must have at least five of the symptoms, one of which must be feeling depressed often or experiencing a loss of interest or pleasure in life.
The symptoms have to adversely affect a person’s social well-being, their job, or other important aspects of their life.
The symptoms that doctors use to diagnose MDD are symptoms of major depressive episodes. For a doctor to recognize the disorder, a person must also have experienced at least two of these episodes separated by at least 2 months.
PDD diagnosis
Doctors likewise use the symptoms of PDD to diagnose the disorder.
To receive the diagnosis, a person must have at least two PDD symptoms —as well as depression or irritability that has lasted for at least 2 years, in adults, or at least 1 year, in children and teens.
These symptoms need to adversely affect a person’s social well-being, their job, or other important areas of their life.
For a person to receive a diagnosis of PDD, the symptoms cannot have been absent for more than 2 months at a time during a 2-year period, in adults, or a 12-month period, in younger people.
Psychiatrists and other doctors use very similar approaches to MDD and PDD treatment.
MDD treatment
There are several treatment options for MDD.
Doctors, including psychiatrists, help determine the most appropriate treatment plan based on the severity and type of symptoms.
For mild MDD, they often recommend psychotherapy and monitoring symptoms. However, a doctor may recommend medication for a person with MDD symptoms of any severity.
Treatments for moderate MDD often include psychotherapy and medication.
Psychotherapy-based treatments include:
- cognitive behavioral therapy (CBT)
- behavioral activation
- interpersonal psychotherapy
Medications for MDD include:
- selective serotonin reuptake inhibitors (SSRIs), such as sertraline (Zoloft) and citalopram (Celexa)
- serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine (Effexor) and duloxetine (Cymbalta)
- other medications, such as bupropion (Wellbutrin) and mirtazapine (Remeron)
Medication usually starts at a low dosage, to be increased if needed. MDD symptoms could improve in as few as 2 weeks, but a person may not be symptom-free before 8–12 weeks have passed.
Using medication and psychotherapy can be more effective than medication alone.
PDD treatment
Treatment for PDD is not significantly different from treatment for MDD. It tends to involve:
- methods of psychotherapy, such as CBT
- medication, including SSRIs or SNRIs
An SSRI is usually the first medication that a psychotherapist prescribes because this type causes slightly fewer side effects than SNRIs.
However, a number of factors go into decisions about medication. Doctors work with people to ensure that the choice and dosage of medication best suits their needs.
PDD and MDD are two forms of depression that have similar symptoms and treatment methods.
The main difference concerns the duration of symptoms. PDD symptoms last for at least 2 years, in adults, while people with MDD experience depressive episodes that are separated by at least 2 months.
Genetic, social, and physical factors cause PDD and MDD. Various parts of the brain play important roles in the development of these disorders.
Treating PDD and MDD may involve methods of psychotherapy, such as CBT, and medications, including SSRIs and SNRIs. These may be especially effective in combination.