Linking plasma cortisol levels to phenotypic heterogeneity of posttraumatic stress symptomatology

Recent confirmatory factor analytic studies of the dimensional structure of posttraumatic stress disorder (PTSD) suggest that this disorder may be best characterized by five symptom dimensions-re-experiencing, avoidance, numbing, dysphoric arousal, and anxious arousal. Hypothalamic-pituitary-adrenal (HPA) axis dysregulation in PTSD and has been attributed to enhanced glucocorticoid responsiveness. However, little is known about how altered HPA-axis function is related to this contemporary phenotypic model of PTSD.

We compared morning plasma cortisol levels of drug-free civilian adults with PTSD (N = 29) to trauma-exposed (TC; N = 12) and non-trauma-exposed healthy controls (HC; N = 23). We then examined the relation between cortisol levels and a contemporary 5-factor 'dysphoric arousal' model of PTSD symptoms among individuals with PTSD.

After adjustment for white race/ethnicity, education, lifetime alcohol use disorder, and current smoking status, the PTSD (Cohen's d = 1.1) and TC (Cohen's d = 1.3) groups had significantly lower cortisol levels than the HC group; cortisol levels did not differ between the TC and PTSD groups. Except for age (r = -.46), none of the other demographic, trauma-related, or clinical variables, including lifetime mood/anxiety disorder and severity of current depressive and anxiety symptoms, were associated with cortisol levels. In a stepwise linear regression analysis, age (β = -.44) and severity of emotional numbing symptoms (β = -.35) were independently associated with cortisol levels in the PTSD group; none of the other PTSD symptom clusters or depression symptoms were significant. Post hoc analyses revealed that severity of the emotional numbing symptom of restricted range of affect (i.e., unable to have loving feelings) was independently related to cortisol levels (β = -.35).

These results suggest that trauma-exposed civilian adults with and without PTSD have significantly lower cortisol levels compared to healthy, non-trauma-exposed adults. They further suggest that low cortisol levels among adults with PTSD may be specifically linked to emotional numbing symptomatology that is unique to the PTSD phenotype and unrelated to depressive symptoms.