A 70-year-old woman presented with severe but minimally painful right glenohumeral osteoarthritis (OA), with progressive weakness and numbness radiating to the right hand. Imaging revealed a large fluid collection extending from the joint to the subcoracoid space, with a mass effect on the brachial plexus. A total shoulder arthroplasty (TSA) and decompression of a ganglion cyst were performed. Follow-up with serial electromyography demonstrated resolution of the brachial plexopathy and restoration of function.
Ganglion cysts may arise secondary to severe glenohumeral OA and may compress the surrounding structures, producing a progressive plexopathy. Treatment of the underlying pathology with a TSA may be effective.