The article describes the case of an 11-year-old boy who showed symptoms of the atrophy at his right shoulder. The child, diagnosed with the right shoulder plexus damage (MRI of the right shoulder plexus and the cervical spine was normal), was sent to EMG laboratory in Bydgoszcz. EMG tests did not show any features of the right shoulder plexus damage. The clinical examination showed the wrong position of the shoulder blade, difficulty with shoulder raising and arm abduction. The atrophy was limited to the trapezius muscle. No dysesthesia was observed. A little scar was located at the lateral cervical triangle, behind the sternocleidomastoid muscle. The scar resulted from the removal of the enlarged lymph node. The shoulder muscles atrophy occurred a few months later. Neither the boy nor his mother associated these events. On the basis of clinical examination and EMG tests the boy was diagnosed with the damage of the eleventh right nerve. The lymph nodes removal at the lateral cervical triangle is the most frequent cause of the accessory nerve damage. Other causes include: cranial basis tumors, basal skull and condylar fractures, accessory nerve neurinoma, carotid artery endarterectomy, internal carotid vein catheterizations, pulling, injury, painful atrophy of the shoulder zone muscles. Main problems with treating traumatic (and iatrogenic) damages of the accessory nerve include wrong diagnosis and conservative therapy. The best results of surgical procedures are obtained up to 3-month period following the injury. Differential diagnosis of the shoulder muscle atrophy should take into account the possibility of the accessory nerve damage. 

brachial plexus, accessory nerve, eleventh nerve, sternocleidomastoid muscle, trapezius muscle