According to Marsha Linehan, many mental health professionals find it challenging to diagnose BPD using the DSM criteria, since these criteria describe such a wide variety of behaviors. To address this issue, Linehan has grouped the symptoms of BPD under five main areas of dysregulation: emotions, behavior, interpersonal relationships, sense of self, and cognition. International Classification of Disease
The World Health Organizations ICD-10 defines a disorder that is conceptually similar to BPD, called (F60.3) Emotionally unstable personality disorder. Its two subtypes are described below. F60.30 Impulsive type
At least three of the following must be present, one of which must be (2):

marked tendency to act unexpectedly and without consideration of the consequences;
marked tendency to engage in quarrelsome behavior and to have conflicts with others, especially when impulsive acts are thwarted or criticized;
liability to outbursts of anger or violence, with inability to control the resulting behavioral explosions;
difficulty in maintaining any course of action that offers no immediate reward;
unstable and capricious (impulsive, whimsical) mood. F60.31 Borderline type
At least three of the symptoms mentioned in F60.30 Impulsive type must be present [see above], with at least two of the following in addition:

disturbances in and uncertainty about self-image, aims, and internal preferences;
liable to become involved in intense and unstable relationships, often leading to emotional crisis;
excessive efforts to avoid abandonment;
recurrent threats or acts of self-harm;
chronic feelings of emptiness;
demonstrates impulsive behavior, e.g., speeding in a car or substance use.The ICD-10 also describes some general criteria that define what is considered a personality disorder. Millons subtypes
American psychologist Theodore Millon has proposed four subtypes of BPD.
A smaller number of studies have used magnetic resonance spectroscopy to explore changes in the concentrations of neurometabolites in certain brain regions of BPD patients, looking specifically at neurometabolites such as N-acetylaspartate, creatine, glutamate-related compounds, and choline-containing compounds.Some studies have identified increased gray matter in areas such as the bilateral supplementary motor area, dentate gyrus, and bilateral precuneus, which extends to the bilateral posterior cingulate cortex (PCC). The hippocampus tends to be smaller in people with BPD, as it is in people with post-traumatic stress disorder (PTSD). However, in BPD, unlike PTSD, the amygdala also tends to be smaller. This unusually strong activity may explain the unusual strength and longevity of fear, sadness, anger, and shame experienced by people with BPD, as well as their heightened sensitivity to displays of these emotions in others. Given its role in regulating emotional arousal, the relative inactivity of the prefrontal cortex might explain the difficulties people with BPD experience in regulating their emotions and responses to stress. Neurobiology
Borderline personality disorder has previously been strongly associated with the occurrence of childhood trauma or ACE (Adverse Childhood Experience). While many psychiatric diagnoses are believed to be associated with traumatic experiences occurring during critical periods of childhood, specific neurobiological factors have been identified within patients diagnosed with BPD. Dysregulations of the hypothalamic-pituitary-adrenal (HPA) axis and cortisol levels have been intensively studied in individuals who have experienced childhood traumas and have been formally diagnosed with BPD.