Recently, the VA announced an interim rule (effective August 4, 2014), and proposed final rule, which incorporates the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria into Title 38. More information about the changes can be found at https://www.federalregister.gov/articles/2014/08/04/2014-18150/schedule-for-rating-disabilities-mental-disorders-and-definition-of-psychosis-for-certain-va.
An informative and straightforward Wikipedia entry was created that both explains Post-Traumatic Stress Disorder (PTSD) in the context of Title 38 and how PTSD is defined under DSM-5. More information can be found at Wikipedia (PTSD).