Defence mechanisms are the automatic psychological responses that individuals use in response to anxiety and internal or external stress and conﬂict (American Psychiatric Association, 1994).
It is baffling why some individuals do not perceive that some traits (e.g. impulsiveness), speciﬁc behaviours (e.g. self-mutilation), self-reported experiences (e.g. feelings of emptiness), and beliefs or cognitions (e.g. grandiose sense of self-importance) are often maladaptive and strive to supplant them with more adaptive ones. The defenses’ avoidance function may supply one answer to this enigma and explain the connection between defence mechanisms and personality disorders (PD).
"Defense Mechanisms in Schizotypal, Borderline, Antisocial, and Narcissistic Personality Disorders" - https://www.researchgate.net/publication/235785471_Defense_Mechanisms_in_Schizotypal_Borderline_Antisocial_and_Narcissistic_Personality_Disorders examines just this - the association between speciﬁc defence mechanisms and four PD types (schizotypal, borderline, antisocial, and narcissistic personality disorder) and considers their potential role in personality functioning.
The authors examined their hypotheses using dynamic interview data rated for defences of 107 participants diagnosed with the four personality disorder types mentioned above.
They found that "the prevalence of immature defenses was substantial, and all four disorders ﬁt within the broad borderline personality organization construct. Defenses predicted the most variance in borderline and the least variance in schizotypal personality disorder, suggesting that dynamic factors played the largest role in borderline and the least in schizotypal personality. Central to borderline personality were strong associations with major image-distorting defenses, primarily splitting of self and other’s images, and the hysterical level defenses, dissociation and repression. Narcissistic and antisocial personality disorders shared minor image-distorting defenses, such as omnipotence or devaluation, while narcissistic also used splitting of self-images and antisocial used disavowal defenses like denial. Overall, differential relationships between speciﬁc defenses and personality disorder types were largely consistent with the literature, and consistent with the importance that the treatment literature ascribes to working with defenses."
This is a relatively old study, so it will be interesting to see any development in this area and how these insights are implemented in treating and preventing PD.