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Stem
A 23-year-old woman is brought to the emergency department after taking an overdose of paracetamol, triggered by her boyfriend of three months ending the relationship. She has multiple healed laceration scars on her left forearm. On interview she describes the boyfriend as "perfect" two weeks ago but now "evil". She reports intense fear of being alone, a chronic sense of emptiness, and brief episodes of feeling "unreal" when stressed. Her mood shifts several times within the hour of the interview, in response to questions about the relationship. There is no prior diagnosis. She works as a teaching assistant but has had several short jobs and two brief psychiatric admissions in the past two years for similar episodes.
Questions
a) What is the most likely diagnosis, and list five DSM-5 criteria that support it? (3 marks)
Model answer. Borderline personality disorder (BPD). Five of nine DSM-5 criteria (need 5 of 9): (1) frantic efforts to avoid real or imagined abandonment; (2) a pattern of unstable and intense relationships characterised by alternating idealisation and devaluation (splitting); (3) identity disturbance / markedly unstable sense of self; (4) impulsivity in at least two self-damaging areas; (5) recurrent suicidal behaviour, gestures, threats, or self-mutilating behaviour (overdose + scars); (6) affective instability due to marked reactivity of mood (minutes-hours, reactive); (7) chronic feelings of emptiness; (8) inappropriate, intense anger or difficulty controlling anger; (9) transient, stress-related paranoid ideation or dissociation. The case demonstrates fear of abandonment, splitting, self-harm, reactive affective instability, emptiness, and transient dissociation — more than five criteria. Onset must be by early adulthood and the pattern enduring and pervasive across contexts.
b) List three conditions you would actively exclude in the differential, with the discriminating feature for each. (3 marks)
Model answer. (1) Bipolar disorder (especially bipolar II) — discriminated by tempo and trigger: BPD mood shifts are minutes-to-hours and reactive to interpersonal triggers; bipolar episodes are sustained (days-weeks) and spontaneous, with normal intervals and a strong family history. (2) Complex post-traumatic stress disorder — shares trauma history, affect dysregulation, dissociation, and self-harm, but lacks the pervasive identity disturbance, splitting, and abandonment-driven impulsivity that are central to BPD (the two can coexist). (3) An organic cause for new personality change — TBI, frontal lobe tumour, endocrine disturbance (thyroid, Cushing), or substance; ruled out because BPD is enduring and traceable to early adulthood, whereas organic personality change is new-onset and demands bloods (FBC/U&E/LFT/TFT/B12/syphilis/HIV), a urine drug screen, and brain imaging if focal/new. (Accept: major depressive disorder — episodic anhedonia/guilt/poor concentration rather than pervasive personality pattern; histrionic PD — shallow affect, no self-harm or identity disturbance.)
c) Outline the definitive management, naming the first-line therapy with its components and the role of medication. (3 marks)
Model answer. First-line and most evidence-based: structured psychotherapy — dialectical behaviour therapy (DBT). DBT structure: weekly individual therapy + weekly group skills training + phone coaching + therapist team meeting, over 12–18 months. The four skills modules are mindfulness, distress tolerance, emotion regulation, and interpersonal effectiveness. Mentalization-based therapy (MBT), schema therapy, transference-focused psychotherapy, and good psychiatric management are alternatives with comparable evidence. Medication is symptom-targeted, not first-line for core traits (per NICE CG78): SSRI (e.g. fluoxetine 20–60 mg PO daily) for affective lability/impulsivity/comorbid depression; mood stabiliser (lamotrigine 25–200 mg PO daily; valproate is contraindicated in women of childbearing potential) for affective instability; low-dose second-generation antipsychotic (olanzapine 2.5–10 mg or aripiprazole 5–15 mg PO daily) for transient psychosis or severe anger. Benzodiazepines are avoided (disinhibition, dependence, overdose risk). Treat comorbid depression, substance use, eating disorders, and PTSD in their own right.
d) Describe the immediate (resuscitative) management of her presentation in the emergency department and one iatrogenic harm to actively avoid. (1 mark)
Model answer. Treat the medical consequences of paracetamol overdose first (paracetamol level at 4 hours, treat with N-acetylcysteine per the treatment nomogram if above the line; check INR, LFT, U&E, glucose, venous blood gas). Provide a safe environment, remove means, observe. Structured suicide-risk assessment (ideation, plan, intent, access to means, protective factors — e.g. C-SSRS). Psychiatric assessment before disposition; safety planning (Stanley-Brown) and 24–48 hour follow-up. Avoid brief reflexive discharge, but also avoid prolonged admissions (which can reinforce self-harm in BPD). Iatrogenic harm to avoid: prescribing benzodiazepines for behavioural dyscontrol (disinhibition, paradoxical agitation, overdose risk), or over-prescribing / polypharmacy; prolonged admissions reinforcing the behaviour; or misdiagnosis as bipolar. Manage splitting with a single care coordinator and team consistency.