How can you differentiate exactly between Reactive Attachment Disorder and 'Pervasive Developmental Disorder'?

I know that Reactive Attachment Disorder, both the inhibitied and the disinhibited (Disinhibited Attachement Disorder, DAD) is an attachment disorder caused by the social environment such as neglect and abuse.



I know that Pervasive Developmental Disorder NOS is on the autistic spectrum and thus considered to be biological in nature rather than caused by the social environement.



My questions is how, when presented with a person to assess does one tell if the person is suffering from RAD or PDD?



What are the differences in behaviour between RAD and PDD?

What are the differences in symptoms between RAD and PDD?



I think that in some cases PDD can display perseverative interests which might not be a symptom of RAD. However, someone with RAD might be going through a difficult time which requires working on an issue at that time, or perhaps the person with RAD has a touch of obsessive personality or maybe OCD. Some with RAD might then be diagnosed with PDD NOS.



What do you think?How can you differentiate exactly between Reactive Attachment Disorder and 'Pervasive Developmental Disorder'?
hard to tell