12th Jan 2023
Borderline personality disorder and narcissistic personality disorder are mental health conditions classified as cluster B personality disorders. The symptoms, interpersonal impairments, and emotionality of these disorders can overlap, making accurate diagnosis difficult.
People with borderline personality disorder (BPD) generally have a history of unstable, intense interpersonal relationships and self-harming, impulsive behaviors. They have difficulty regulating their emotions and experience dramatic, rapid fluctuations in mood.
Symptoms of personality disorders including BPD must be present before adulthood and cause marked distress in everyday life for diagnosis. Someone can have traits of BPD without meeting the diagnostic threshold.
A fear of abandonment is at the core of BPD, with most other symptoms arising as unhealthy coping strategies to prevent this. Others may describe them as "clingy" or as constantly needing validation.
Someone with BPD may fluctuate from idolizing a loved one to devaluing them as a person when feeling criticized or pushed away. Many with this disorder report feelings of emptiness when alone, have low self-esteem, and believe they are unworthy of love.
Emotional dysregulation may manifest as intense anger outbursts or rage episodes, followed by painful shame and guilt feelings that further perpetuate low self-esteem and negative self-beliefs.
Impulsivity in BPD is typically observable in self-harming ways, such as excessive gambling, unsafe sex practices, substance abuse, self-injurious behaviors, and suicide.
People with BPD may experience times when their symptoms are low and manageable. Stress is known to worsen the symptoms of this disorder.
Historically, stigma has surrounded personality disorders. Research has helped mental health professionals better understand the causes and underlying components of these disorders.
It is important to know that people with BPD are living with immense pain and hurt nearly all the time. Many of the behaviors impeding stable interpersonal relationships can be considered unhealthy attempts to create attachment and connection to others to avoid loneliness or abandonment.
People with BPD often genuinely want to connect and be connected to others. They may feel as confused by the rapid changes in their mood and dangerous impulses as their loved ones do.
People with narcissistic personality disorder (NPD) have a pattern of grandiose thinking, exploitative behavior, and lacking or diminished empathy for how their actions impact others. These behaviors and beliefs cause impairments in relationships, employment, and daily interactions with others.
Underneath these beliefs of superiority and grandiosity, people with NPD may have a fragile ego with an underlying fear of being worthless.  If this is true, their behavior can be considered an unhealthy way of preventing others from seeing the "real" them.
Those with NPD strive to maintain the illusion of high self-esteem and ego.
Narcissistic personality disorder symptoms include: 
Others may find those with NPD to be moody, impatient, easy to anger, and dominating.  They may become enraged by minor critiques.
They are likely to be emotionally unavailable in relationships, though they can be very charming initially.  People with NPD have a higher likelihood of abuse towards romantic partners because of their need for power and control.
Narcissistic personality disorder commonly occurs comorbidly with other personality disorders or mental health conditions such as substance use disorders or bipolar disorder. These comorbid conditions are more likely to be what brings them into treatment.
People with NPD seek constant flattery from others to fuel their egos. They can quickly react with vengeful behaviors when they feel slighted or criticized.
People with NPD rarely take accountability for how their behavior affects others. They have difficulty recognizing that others have their own desires, feelings, and thoughts, and assume that everyone is out for themselves. 
BPD and NPD both cause impairments in interpersonal relationships. There is significant overlap in how the symptoms of BPD and NPD present and impact daily functioning. It is also possible for someone to have characteristics of both disorders.
Both disorders can cause exaggerated emotional reactions to minor criticisms or conflict that can be frightening and confusing for loved ones.
Those with BPD are more likely to experience shame due to their emotional outbursts, whereas those with NPD are more likely to believe their reaction was justifiable.
The key differences between the two disorders are the underlying motivations for the behavior.
Controlling others and the environment is an unhealthy strategy that those with BPD or NPD may implement.
People with BPD or NPD may have difficulty maintaining employment, friendships, or meeting other life expectations. People with either disorder tend to play the victim when expectations are not met or during a conflict with others.
Both disorders have a component of insecurity and fear at the core. 
People with BPD are terrified of abandonment and being alone, whereas people with NPD are fearful of people figuring out they are "unworthy" and seeing their flaws.
Unhealthy coping and defense mechanisms based on thinking errors, such as black-and-white thinking, are ways that those with either disorder attempt to navigate their fear.
People with BPD are more likely to self-harm, have suicidal thoughts, and outwardly appear vulnerable. They also genuinely desire to connect and form attachments to others. 
Those with NPD rely on excessive flattery from others to satisfy their ego, vengeful reactions, and exploitative behaviors to meet their needs.
The causes of BPD or NPD remain a widely under-researched area of psychology. Personality disorders, in general, are believed to be caused by a combination of genes and environmental factors.
Borderline personality disorder is currently more widely understood than narcissistic personality disorder. This may largely be due to people with BPD being more likely to seek and remain in treatment than those with NPD.
Childhood adverse experiences, particularly childhood sexual abuse and neglect, are linked to the development of BPD. 
It is now known and understood that maltreatment in childhood, including neglect, can cause permanent changes in how the brain develops.
Brain studies have found less grey matter in the brains of participants with NPD compared to control groups. Brain scans also have shown hippocampus and amygdala damage in those with NPD. 
These emerging results indicate that there are biological components to NPD behaviors.
Parenting and attachment to caregivers play a large role in the development of personality disorders. Studies have shown children who experience neglect or inconsistent feedback from caregivers are at risk of developing traits associated with both BPD and NPD. 
Borderline personality disorder and narcissistic personality disorder are considered chronic conditions requiring long-term mental health treatment.
There is scant research available on treatment for NPD, primarily because people with this disorder are unlikely to seek treatment for the disorder. They may instead seek treatment for comorbid conditions such as depression, anxiety, or substance use.
Psychotherapy is considered the treatment of choice for both NPD and BPD.
Dialectical behavioral therapy, or DBT, is the most widely recommended psychotherapy approach for treating BPD. DBT is a form of cognitive behavioral therapy that focuses on skills building for emotional regulation, impulse control, and distress tolerance.
Additional psychotherapy approaches for BPD include: 
These approaches may also prove helpful in treating NPD, as so many of the symptoms overlap.  There is currently no evidence-based recommended treatment for NPD.
Therapy approaches that focus on identifying and challenging defense mechanisms may help with identifying the underlying vulnerabilities for both of these disorders. 
A strong therapeutic alliance is critical for successful treatment through psychotherapy because of the role unhealthy interpersonal attachment and childhood neglect play in the development of these conditions.
Psychopharmacology may also be used conjunctly with psychotherapy to treat underlying mood disorder symptoms for those with either BPD or NPD. Medications used may include mood stabilizers, antidepressants, and anti-anxiety medication.