One Quintillion Ways to Have PTSD Comorbidity: Recommendations for the Disordered DSM-5

Galatzer-Levy and Bryant (Perspect Psychol Sci 8:651–662, 2013) have calculated the number of ways that Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5; American Psychiatric Association, 2013) posttraumatic stress disorder (PTSD) symptoms can be combined as over 600,000. They concluded that the amount is astounding and the category is rendered amorphous. PTSD often occurs in the context of polytrauma or comorbidity. The epidemiological literature indicates that the most common comorbid conditions in cases of PTSD include major depressive disorder (MDD), chronic pain, neurocognitive disorder due to traumatic brain injury (e.g., mild), and alcohol use disorder, with premorbid personality disorder possible, as well (which we consider as exacerbated due to the traumatic incident at issue, as in borderline personality disorder). We calculated the possible symptom combinations for each of these disorders and then in comorbid combination with PTSD (e.g., PTSD with MDD, but also when all six conditions are present). The number of symptom combinations in full polytrauma involving all six conditions listed is truly astounding, over one quintillion. Also, we reviewed the range of PTSD comorbidities, which adds to the symptom heterogeneity in cases. We make recommendations to prioritize symptoms in disorders as primary (e.g., unique, marker), secondary (e.g., core essential), and tertiary (e.g., common, cross-diagnostic). The latter tertiary type of symptoms in a disorder, if any, should be kept apart in its own criterion. This approach might help make the next version of the DSM more clinically useful both to clinicians and to court.