Hi
All responses to date are on target. T4 syndrome is certainly relevant, as is the work posture. As most people tend to slump after prolonged sitting at work stations or driving, a chin poke thoracic kyphotic posture with cervical extension develops. Over time, the musculature holds this position, and the body senses the slump as the least tension point. When such a patient tries to sit up, some muscle groups feed back that tension has increased, and other muscular groups are deficient in their ability to sustain the posture (poor endurance), resulting to a return to the slump.
I find that a progressive exercise to build the rhomboid strength and endurance, whilst stretching the pectorals, and at the same time realigning the cervical curves, is very successful.

Each week over 7 weeks, the patient increases one of three parameters, leading to rhomboid shortening and increased endurance, etc, plus reinforces a new postural habit. In the first 7 - 10 days the patient may experience an increase in symptoms of headache and muscle soreness, but this will pass. They need to be warned, and persevere through bthe changes, as this feeds back the changes.

In sitting or standing, the patient looks straight ahead (to do this in front of a mirror for the first week),and elevates the arms to 90 degres of sh. abduction, and 90 degrees of elbow flexion, so that the arms are parallel with the floor. advise the patient to retract the shoulders, keeping the arms parallel with the floor, and not to jut the chin forward, hold the contraction for 3 seconds without the elbows dropping, and repeat three times, three times daily. The second week hold for 4 seconds, three times, three times daily. Once 5 second hold is reached, the next progression is to repeat four times in the fourth week for 5 seconds, three times per day. With this progression, by week 7, the patient is holding the retracted position for 5 seconds, repeating 5 times per session, 5 times per day. Yes, I give them a handout with instructions and a drawing!

The above exercise is actually very simple, and addresses many problems related to the cervical and thoracic spine, which cause upper limb dysfunction and headaches.
Let me know your thoughts.
MrPhysio