Educational Disclaimer: This case study is for educational and informational purposes only. It does not constitute medical advice, clinical guidance, or a substitute for professional psychiatric evaluation. All diagnostic criteria referenced are from the DSM-5-TR (APA, 2022). Clinical statistics cited are drawn from peer-reviewed literature and may vary across populations. Clinicians should rely on their professional training, direct patient assessment, and current evidence-based guidelines when making diagnostic and treatment decisions.

Clinical Vignette

Patient: "Ms. K," 29-year-old graphic designer, referred by her therapist after 18 months of trauma-focused therapy produced limited improvement. Her therapist suspects a dissociative condition beyond standard PTSD.

Chief Complaint: "I lose chunks of time. Sometimes I find things I've bought but don't remember buying. My friends say I act like a different person sometimes."

History of Present Illness: Ms. K reports three categories of symptoms: (1) Time loss: Periods of minutes to hours where she "comes to" without memory of what occurred (not substance-related, confirmed by PEth and UDS). She finds completed artwork she does not remember creating. Her phone shows sent messages in writing styles she does not recognize. Coworkers describe conversations she has no recollection of. (2) Identity shifts: She describes sudden changes in her preferences (food, music, clothing) and demeanor. Her best friend reports that she sometimes speaks in a "younger voice" and becomes fearful of adult men. At other times, she becomes assertive and confrontational in a manner inconsistent with her baseline personality. She reports hearing internal "arguments" between different "parts" of herself. (3) Trauma re-experiencing: Intrusive memories of physical and sexual abuse by a family member (ages 5-12). Nightmares 3-4 nights per week. Hypervigilance in enclosed spaces. Avoidance of the family member's geographic area.

Key Observation: During the interview, Ms. K's affect, posture, and speech pattern shift noticeably. At one point, she becomes guarded, speaks in shorter sentences, and refuses to discuss childhood history. After several minutes, she "returns" and apologizes, stating "I don't know what just happened." She does not recall what she said during the previous few minutes.

Psychiatric History: Previous diagnoses: PTSD (age 23), Major Depressive Disorder (age 21). Treated with sertraline (partial response for depression, no effect on dissociative symptoms) and trauma-focused CBT (limited by her inability to maintain continuity across sessions). No substance use disorder. No psychotic symptoms reported or observed.

Mental Status Exam: Variable during interview: alternates between cooperative, guarded, and briefly tearful. Affect shifts from constricted to anxious to flat within the session. Speech is at times rapid, at times hesitant. Thought process logical when engaged. No delusions or hallucinations (other than internal "voices" described as arguing). Oriented to time, place, person. Denies suicidal ideation.

Step 1: Ruling Out Non-Dissociative Explanations

Before evaluating DID, the clinician must exclude:

Substance-Induced Amnesia: PEth (phosphatidylethanol) and UDS negative. No alcohol blackouts or substance-induced memory gaps. EXCLUDED.

Seizure Disorder (esp. temporal lobe epilepsy): No postictal confusion, tongue biting, incontinence, or tonic-clonic activity reported. EEG recommended to formally exclude. PROVISIONALLY EXCLUDED; EEG recommended.

Traumatic Brain Injury: No history of head trauma with loss of consciousness. EXCLUDED.

Malingering/Factitious Disorder: No secondary gain identified (not in forensic context, no disability claim). Symptoms are distressing and ego-dystonic. Therapist has observed in-session switching over 18 months. LOW PROBABILITY.

Step 2: DID vs. PTSD with Dissociative Subtype

Feature DID PTSD (Dissociative Subtype) This Patient
Identity disruption ≥2 distinct personality states with discontinuity in sense of self and agency Intact identity; dissociation is limited to depersonalization/derealization DID: distinct shifts in speech, behavior, preferences; "parts" with different ages/demeanors
Amnesia pattern Recurrent gaps for everyday events; finding evidence of actions not recalled Amnesia limited to traumatic events (Criterion D1 of PTSD) DID: amnesia for everyday events (artwork, messages, conversations)
Internal voices Common: internal dialogue between parts; experienced within the head Uncommon; if present, limited to traumatic flashback content DID: internal "arguments" between "parts"
Depersonalization/Derealization Present as one feature among many Primary dissociative feature; must be prominent for subtype diagnosis Present, but secondary to identity disruption
Observable switching May be observable or covert; shifts in demeanor, voice, posture No switching; dissociation manifests as detachment/numbing DID: observable shift during interview; therapist-confirmed over 18 months

Step 3: DSM-5-TR Criteria for DID (300.14 / F44.81)

Criterion A: Disruption of identity characterized by two or more distinct personality states, involving marked discontinuity in sense of self and sense of agency, accompanied by related alterations in affect, behavior, consciousness, memory, perception, cognition, and/or sensory-motor functioning.

Ms. K demonstrates: (a) a baseline adult state, (b) a "younger" state with fearful affect and altered voice, (c) an assertive/confrontational state inconsistent with baseline. These are accompanied by shifts in affect (anxious → flat → guarded), behavior (cooperative → refusing), and consciousness (amnesia for switched states). MET.

Criterion B: Recurrent gaps in the recall of everyday events, important personal information, and/or traumatic events that are inconsistent with ordinary forgetting.

Time loss for everyday activities (creating artwork, sending messages, having conversations). Amnesia for in-session switching. Amnesia also present for traumatic events. MET.

Criterion C: The symptoms cause clinically significant distress or impairment in functioning.

Unable to maintain therapeutic continuity. Interpersonal confusion from inconsistent behavior. Distressed by time loss and finding evidence of unremembered actions. MET.

Criterion D: The disturbance is not a normal part of a broadly accepted cultural or religious practice.

No cultural context for the symptoms. MET.

Criterion E: The symptoms are not attributable to the physiological effects of a substance or another medical condition.

Negative substance screening. No seizure disorder, TBI, or medical etiology identified. MET.

Diagnostic Conclusion

Dissociative Identity Disorder (F44.81)

All 5 DSM-5-TR criteria for DID are met. The presentation exceeds the scope of PTSD with dissociative subtype because the dissociative symptoms involve identity disruption (distinct personality states) and amnesia for everyday events, both of which go beyond the depersonalization/derealization that defines the PTSD dissociative subtype.

Comorbid Diagnosis: PTSD (F43.10) is also present (re-experiencing, avoidance, hyperarousal criteria all met). DID and PTSD commonly co-occur. The PTSD is conceptualized as a comorbid condition rather than the primary explanation for the dissociative symptoms.

Teaching Points

  • The PTSD dissociative subtype (introduced in DSM-5) captures patients whose primary dissociative feature is depersonalization or derealization. It does not capture identity disruption or amnesia for everyday events. When these features are present, a separate dissociative disorder (DID or OSDD) must be evaluated.
  • Internal voices in DID are typically experienced as coming from within the head (pseudohallucinations), are recognizable as "parts" of the self (even if disowned), and often engage in commentary or conflict. This contrasts with psychotic auditory hallucinations, which are experienced as coming from outside the head and are attributed to an external source.
  • Observable switching is present in only a minority of DID cases. The DSM-5-TR notes that DID often presents in a "covert" form where identity states are not immediately apparent to the observer. The clinician should assess through structured interview (e.g., SCID-D) and longitudinal observation rather than relying on dramatic in-session switching.
  • Treatment for DID follows a phase-oriented model: (Phase 1) stabilization and safety, (Phase 2) trauma processing (only when the patient can maintain dual awareness), (Phase 3) integration/resolution. Premature trauma processing without stabilization risks destabilization and symptom exacerbation.
  • Malingering should be considered but not assumed. The presence of consistent findings across 18 months of therapy, absence of secondary gain, ego-dystonic distress, and in-session observations by a trained therapist all argue against malingering in this case.