A client has been diagnosed with post-traumatic stress disorder (PTSD) following a motor vehicle accident. Which symptom cluster is MOST characteristic of PTSD?

PTSD is a trauma- and stressor-related disorder defined by four symptom clusters (DSM-5), all present for more than 1 month following exposure to actual or threatened death, serious injury, or sexual violence: (1) RE-EXPERIENCING (INTRUSION): flashbacks (reliving the trauma as if it is happening now, with sensory components — not just a memory); nightmares; intrusive unwanted memories; distress at trauma-related cues; physiological reactions to cues; (2) AVOIDANCE: of trauma-related thoughts or feelings; of external reminders (places, people, activities, conversations, situations that trigger memories); (3) NEGATIVE ALTERATIONS IN COGNITIONS AND MOOD: distorted blame of self or others for the trauma; persistent negative emotions (fear, horror, anger, guilt, shame); diminished interest in activities; feeling detached from others; inability to experience positive emotions (emotional numbing); (4) ALTERATIONS IN AROUSAL AND REACTIVITY: hypervigilance (scanning environment for danger); exaggerated startle response; irritability/aggression; difficulty concentrating; self-destructive behavior; sleep disturbance. ACUTE STRESS DISORDER: same symptoms but duration of 3 days to 1 month post-trauma; if it persists beyond 1 month → PTSD. TREATMENT: trauma-focused CBT (including Prolonged Exposure and Cognitive Processing Therapy); EMDR (Eye Movement Desensitization and Reprocessing); SSRIs and SNRIs; safety first (self-harm, suicidality risk). NURSING APPROACH: establish therapeutic relationship; provide predictable, safe environment; psychoeducation about PTSD; avoid re-traumatizing; trauma-informed care principles; screen for co-occurring conditions (depression, substance use disorder common with PTSD).