Severe brachial plexopathy after an ultrasound-guided single-injection nerve block for total shoulder arthroplasty in a patient with multiple sclerosis: what is the likely cause of this complication?

• 一个全肩关节造行术的多发性硬化的病人，进行了单次注射的神经阻滞后发生了严重的臂丛病变：这个并发症的最可能的原因是什么呢？