## Borderline Personality Disorder (BPD) Classification and Features ### Cluster B Membership **Key Point:** Borderline personality disorder is a Cluster B disorder, grouped with Antisocial, Histrionic, and Narcissistic personality disorders based on shared dramatic, emotional, and erratic presentation patterns. ### Core Diagnostic Features of BPD According to DSM-5, BPD is characterized by a pervasive pattern of instability across **five domains**: 1. **Interpersonal relationships** — intense, unstable, alternating between idealization and devaluation 2. **Self-image** — unstable, rapidly shifting self-concept 3. **Affect regulation** — marked affective instability with intense, brief episodes of dysphoria, anxiety, or irritability 4. **Impulsivity** — recurrent engagement in at least two potentially self-damaging behaviors (substance abuse, binge eating, reckless driving, binge spending) 5. **Suicidality/self-harm** — recurrent suicidal threats, gestures, attempts, or self-harm behavior **High-Yield:** The **instability** across relationships, mood, and behavior is the hallmark of BPD—not a fixed trait but a pattern of rapid, intense fluctuations. This distinguishes BPD from Cluster A (fixed, stable odd beliefs) and Cluster C (stable anxiety and avoidance). **Clinical Pearl:** BPD patients often present with acute suicidal crises, non-suicidal self-injury (NSSI), and relationship conflicts. Dialectical Behavior Therapy (DBT) is the gold-standard psychotherapy. **Mnemonic for BPD Core Features:** **I.R.I.S.** = **I**nterpersonal instability, **R**elationship intensity, **I**mpulsivity, **S**uicidality/Self-harm (with affect instability as the emotional backdrop).
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