Internalizing and externalizing subtypes in female patients with co-occurring post-traumatic stress disorder and substance use disorders

Background: Research has described subtypes with more internalizing and more externalizing symptoms in samples of patients with post-traumatic stress disorder (PTSD) and samples of patients with substance use disorders (SUD). Objective: This study sought to examine the respective subtypes in female PTSD-SUD patients and potential relationships with substance use characteristics. Methods: We performed a latent class analysis (LCA) in 343 adult female participants of a multisite therapy trial on PTSD and SUD. We derived externalizing symptoms from the Assessment of DSM-IV Personality Disorders (ADP-IV) questionnaire. We assessed internalization using the Symptom Checklist-27 (SCL-27) and the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I). We collected substance use-related information using the Addiction Severity Index-Lite (ASI-lite). Results: LCA suggested four latent classes including an externalizing (10.8%), a moderately internalizing class (31.0%), and a highly internalizing class (22.0%), as well as a class with a low severity of psychological symptoms (36.3%). Externalizing participants used more substances than any other class, while the duration of substance use did not differ between groups. Regular use started at a significantly younger age among the members of the highly internalizing subgroup compared to the moderately internalizing and low severity participants, but at an older age compared to the externalizing group members. Conclusions: The finding of two internalizing subgroups along with an externalizing and a low severity class emphasizes the heterogeneity and complexity of populations with PTSD and SUD. This heterogeneity bears implications for research among this group of patients, but also for their treatment, especially considering our results on differences in substance use.