What is the relationship between post-traumatic stress disorder and fugue states? The introduction of the new edition of the Diagnostic and Statistical Manual for Mental Disorders ("DSM-5") is on the horizon.  With it are coming some new, evidence-based diagnoses for dissociative disorders [1], which include conditions such as dissociative fugue (which will now be classified as dissociative amnesia) and dissociative identity disorder.

Fugue states have always been fascinating to me, Wikipedia states that they are


  a rare psychiatric disorder characterized by reversible amnesia for personal identity, including the memories, personality and other identifying characteristics of individuality...Fugues are usually precipitated by a stressful episode, and upon recovery there may be amnesia for the original stressor.


Post-traumatic stress disorder is also precipitated by a stressful (and potentially life threatening) episode, and causes anxiety and autonomic hyperexcitablity.

I've never seen anything written about the level of stressor that can induce a fugue state, but based on their common etiology, I would assume that PTSD and fugue states are related psychologically and neurologically.

To what extent is this true, are these two seemingly different end products of the same initial event?  Is there an anatomical substrate that is common to both?  Does changing the status of "dissociative fugue" -> "dissociative amnesia" mean they should be considered in isolation?


  [1] Spiegel, D., Loewenstein, R. J., et al. (2011), Dissociative disorders in DSM-5. Depress. Anxiety, 28: E17–E45. doi: 10.1002/da.20923
Dissociative Disorders are really fascinating to me as well. Fugue states/episodes as well as dissociative identity disorder (multiple personality disorder) in particular.

PTSD must be differentiated from disorders that can exhibit phenomenological similarities, such as borderline personality disorder and dissociative disorders (including dissociative amnesia). I include borderline personality disorder because it is [particularly] difficult to distinguish from PTSD, and the two can coexist or even be causally related!

A stressor or traumatic event is the causative factor in the development of PTSD, by definition. As people respond to events as being traumatic differently, the stressor alone is not sufficient enough to cause the disorder. In this case, the presence of intense fear or horror is necessary. The clinical features of PTSD include avoidance and emotional numbing, among other things, and patients may present dissociative states, which is the focus of this topic.


  "Patients with dissociative disorders do not usually have the degree
  of avoidance behavior, autonomic hyperarousal, or history of trauma
  that patients with PTSD report."


An essential feature of dissociative amnesia is "an inability to recall important personal information, usually of a traumatic or stressful nature". As in this (as well as borderline personality disorder and PTSD) disorder, many patients have histories of prior abuse or trauma.

Symptoms found only in dissociative amnesia include features of recurrent blackouts, fugue states/episodes, fluctuations in skills, habits, and knowledge. Patients presenting PTSD and/or with borderline personality disorder usually don't present these symptoms. The common factor/symptom is the possible presence of dissociative episodes/states, though they may be precipitated by differing presentation of stressors.

Patients with borderline personality disorder can present transient or short-lived dissociative (or even psychotic) episodes that are almost "circumscribed, fleeting, or doubtful".

Sorry, now I worry I may not have properly answered your question(s). Liken to how different stressors or traumatic events can be experienced in varying degrees in different people, different people can cope or respond differently to them as well. PTSD (like hypervigilance), borderline personality disorder (intense black-and-white thinking, emotional lability), and dissociative disorders (amnesia, blackouts, etc.).

References


DSM-V Post-Traumatic Stress Disorder
DSM-V Dissociative Amnesia
Kaplan and Sadock's Synopsis of Psychiatry