Numbness and tingling are common symptoms in the arm often associated with the use of a keyboard or mouse. However, distinguishing where a nerve is trapped in the arm or neck can be tricky both on clincal examination and with special tests or scans. The history of the pattern of the symptoms is often the most accurate factor in making the diagnosis between the common condition of carpal tunnel syndrome and causes higher up the arm. When it is not obviously carpal tunnel syndrome then the next commonest condition is 'thoracic outlet syndrome'. The usual cause of this condition is the insidious development of poor postural habits over many years. Because it is a difficult condition to diagnose, it has generated considerable controversy in the medical world.
I do not propose to go into detail with this condition as there are a number of good reviews available to the interested person, including the following links.
The diagnosis may be difficult to make but as the mainstay of treatment is physiotherapy I usually recommend this modality initially, looking specifically at the posture of the patient and then introducing postural re-education and neural stretching exercises. If this fails after an adequate period of treatment (often 2-3 months) then I will institute investigations. The surgical causes of the condition are rare so it does not make sense to investigate everyone.