Which disorder involves significant interpersonal problems including inappropriate affect?

The disorder characterized by significant interpersonal problems and inappropriate affect is borderline personality disorder. This condition is marked by a pattern of unstable interpersonal relationships, self-image, and affect, leading to marked impulsivity. Individuals with borderline personality disorder often experience intense emotional reactions that can result in inappropriate or exaggerated facial expressions and responses that are not proportional to the situation.

Moreover, those with borderline personality disorder may struggle with maintaining stable relationships due to their fears of abandonment and intense emotional fluctuations. They can exhibit a mix of idealization and devaluation toward others, further complicating interpersonal interactions.

In contrast, the other disorders listed do not primarily feature the combination of significant interpersonal problems coupled with inappropriate affect to the same degree. For instance, schizotypal personality disorder typically involves cognitive distortions and eccentric behavior, rather than the emotional instability seen in borderline personality disorder. Paranoid personality disorder is characterized by pervasive distrust and suspicion of others, which doesn't include inappropriate affect as a primary feature. Finally, avoidant personality disorder focuses on social inhibition and feelings of inadequacy, leading to avoidance of social interactions, but does not center around inappropriate emotional responses.