Could also be a minor nerve issue, or pec minor issue.

I'm curious what types of things PT was doing or having him do?
*weights/strengthening - poor PT can often be a bad thing for TOS..*
some PTs are much better assessing what needs are than others..and how to proceed without worsening.

Some home care ideas..
Sharon Butler - Repetitive Strain Injury (gentle stretching /fascia info)
Trigger point release - can do self w/ tennis ball or similar - a wall or floor works
far infra-red heating pad
someone that does low level laser/cold laser/soft laser (same thing but called by all those names.). check /call & ask @ chiro or PT places..if interested in soft laser & IF stim
ultrasound can be used to help with some scarring & soft tissue healing.

corpse pose /relaxation on floor
opposite position stretches -- arms are usually forward of body most of the day - so place them behind and hold 30 sec many times a day don't force it tho..


TOS sticky threads-
Trigger point information {TrPs} for short
https://www.neurotalk.org/thoracic-o...les-polls.html
DOCTORS & PTs List and saved PT info threads