Pain from injury to the brachial plexus or peripheral nerves can mimic pain of cervical spine origin. Neoplastic infiltration can produce this syndrome, as can postradiation fibrosis (pain less often present). Acute brachial neuritis consists of acute onset of severe shoulder or scapular pain followed over days by weakness of proximal arm and shoulder girdle muscles innervated by the upper brachial plexus; onset often preceded by an infection or immunization.