Unilateral reduction of the cervical response in median SEP due to a vertebral fracture, unrecognized in plain films

We report on a patient presenting with hypaesthesia in first, second and third finger of the right hand following a motorcycle accident. Conventional X-ray showed only a mild dislocation in C6/C7 segment. Cervical MRI in order to prove a root avulsion, was reported to be normal. Somatosensory evoked potentials (SEP) revealed a reduced amplitude of the cervical response on right median nerve stimulation. Needle-EMG showed a mild reduced recruitment pattern in triceps brachii muscle compatible with an anterior root lesion. Reviewing MRI, a signal loss in the course of C7 root was suspicious for an articular process fracture. This was proved in a CT scan. This case report emphasizes the topodiagnostic value of the reduced amplitude of the cervical potential of median nerve SEP and the importance of the CT in evaluating cervical spine fractures, as plain films frequent fail to do so.