The best evidence your son can have are Dr's that agree with his request for SSDI.I'm not sure how Dr's that SSA send you to accept applicants for SSDI.Bottom line is,your son needs to have "his"Dr.help him along the way as best as possible. Depending on many things he may or may not be approved at the application phase. So it's probably best not tgo assume approval.Age is a big factor as well. I have been going through the system fo 3 and a half yrs now. Live in FL.which is one of the most inefficant states regarding SSDI.I am awaiting my hearing.I have 3 herniated disks,stenosis,facet joint syndrome.Severe arthritis in both knees.Toe and finger joints with severe arthritis.I take opiates for pain control,sleep aids,depression drugs.I need procedures every 8-12 months to lessen back pain,had 3 knee surgeries in last 5 yrs,need another one,probable knee replacement,toe joint replacements done a couple yrs ago,yada yada yada,still got denied 2x and numerous DR's have agreed I am perm. total disabled. Its a tough system and for most takes years to be finally awarded the SSDI.Good luck to your son,in the event he be denied,he needs to contact an atty.immediatly to ontinue the fight.