Unilateral Pectoral atrophy

Dear Ask The Doctor: Hi there, im a healthy 29 year old male. my problem is that only one of my pecks has muscle. its really strange and embarrassing. my left peck is fine and i have alot of strenght in it but my right is totally flat and week. i only really started to notice this problem 4 or 5 years ago when i started to do weights and work out,now cant stand to look at myself in the mirror. i really need help as i cant find any info on this anywhere on the net. i was with my gp but he basically said its was just one of those things.please help gavin

Dear Gavin: According to your description, it would be important to rule out a cervical radicular compression, in other words a pinched nerve at the cervical spine level, on the right side that is producing such atrophic change in your right pectoral. On the other hand, there are few description in the medical literature of  cases of isolated damage to a muscle branch of the lateral pectoral nerve. In the few reported cases of such injuries, the cause was trauma to this region. However, focal muscle atrophy gradually developed after initiation of training schedules to increase the cross-section of the major pectoral muscle. The fact that the atrophy is asymmetric, and that you are quite or almost asymptomatic makes me rule out any  progressive heredofamilial myopathies, or of mild or gradually progressive heredofamilial or degenerative disorders of nerves or anterior horn cells of the spine.