An MRI of the cervical spine would be the next test I would consider. Any type of disc herniation can lead to the tingling in the the thumb, and forearm. The MRI is the most comprehensive test to diagnose this.
You may want to discuss this with your personal physician, or obtain a neurosurgery consult.
As to how it can affect your career - this would depend on what is found on further evaluation. Normally, herniated discs (if present), can be treated conservatively with physical therapy. There are a minority that don't get better and require surgery or epidural injections.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b