Well, actually there are differences in symptoms and people with BPD can also have PTSD from childhood abuse.

At one time there was an arguement about making BPD something like chronic PTSD and extending some of the symptoms, since the majority of BPD clients have reported abuse in their past.

PTSD includes Flashback and things like re-experiencing the event, avoiding the event, etc. BPD does not directly mention these symptoms. Also, BPD has a big issue with abandonment, whereas PTSD may not necessarily have.

Both may have dissociation, self-harm, depression, anxiety.