I am a bit confused. In an open access article (Caspi, et al. 2020), is the following — under Methods: Assessing Psychopathology (emphasis mine):
[...] externalizing disorders (ie, attention-deficit/hyperactivity disorder, conduct disorder, alcohol dependence, cannabis dependence, other drug dependence, and tobacco dependence), internalizing disorders (ie, depression, generalized anxiety disorder, fears [including social phobia, simple phobia, agoraphobia, and panic disorder], posttraumatic stress disorder, and eating disorders [including bulimia and anorexia]), and thought disorders (ie, obsessive-compulsive disorder, mania, and schizophrenia)
I can understand that PTSD will be caused by internalisation of the trauma experience(s), but from my experience, elements of PTSD often involve externalising (hypervigilence for example) and sometimes unhelpful thoughts/behaviours (for example, fear of all people of a certain religion, culture, background and/or gender; and to the extreme, violent tendencies towards those people to "prevent" further traumatising events).
So is PTSD just an internalising disorder, or can it be a mixture of an internalising, externalising and thought/behaviour disorder?
Caspi, A., Houts, R. M., Ambler, A., Danese, A., Elliott, M. L., Hariri, A., ... & Rasmussen, L. J. H. (2020). Longitudinal Assessment of Mental Health Disorders and Comorbidities Across 4 Decades Among Participants in the Dunedin Birth Cohort Study. JAMA Network Open, 3(4), e203221-e203221. https://doi.org/10.1001/jamanetworkopen.2020.3221