Quick Consult. Shoulder MRI. 62F 3_4 months pain and limited range of motion

I figure it has to be Parsonage Turner if it is indeed denervation otherwise a myositis (in the absence of any trauma history). In this case it is interesting that the axillary (deltoid/teres minor) spinal accessory (trapezius), suprascapular (supraspinatus and part of the infraspinatus) and upper and lower subscapular nerves would have to be involved if denervation so the alternate name for P.T. of idiopathic brachial plexitis would make sense (although the spinal accessory isn’t part of the brachial plexus! I think it is meant to say any nerve works for this diagnosis).

As far as the segmental part of the question, it would make sense that it could be different innervation within a single muscle because there is variation in the human body and there is innervation from different nerves reported especially in the upper extremity including the forearm and hand (trying to keep away from my own observations which we know can be unreliable).