I was going to guess a right C5 radiculopathy given the atrophy of the deltoid, biceps, and pectoralis major. However, the right trapezius seems smaller as well which would invoke a C3/C4 or accessory nerve injury. Therefore, to have a polyradiculopathy seems less likely. It may just be disuse secondary to a pec tear but you can see the triceps and latissimus on the right are well developed. A proximal myopathy would be unusual unilaterally but the thought of limb girdle muscular dystrophy did cross my mind.