A Case Report of Lumbosacral Plexopathy in a Patient with a History of Sacral Chordoma and Radiotherapy: Will the Detection of Myokymia on the EMG Help to Solve the Case?1

BACKGROUND: When a patient with a prior history of malignancy and radiotherapy develops progressive weakness as a presentation of plexus involvement, the differential diagnosis usually rests between radiation-induced plexopathy and invasion from recurrent tumor. The presence of myokymic discharges is helpful in differentiating radiation-induced from neoplastic plexopathy. OBJECTIVE: To present a case report of a patient with chordoma, a locally aggressive tumor, who was diagnosed with recurrent tumor accompanied by the occurrence of myokymia in needle electromyographic examination. METHOD: A 55-year-old male patient with a history of chordoma and radiotherapy presented to our outpatient clinic with complaints of foot drop, and impaired walking for two months. His latest magnetic resonance imaging (MRI) which was performed three months earlier did not show recurrence. Upon electromyographic evaluation, myokymia, the pathognomic electromyography abnormal wave for radiation plexopathy was detected supporting a diagnosis of radiation plexitis rather than recurrent neoplastic invasion. One month later he presented with more severe pain and was re-evaluated by an MRI, on which a mass was detected indicating relapse. CONCLUSION: With this case report, we would like to emphasize that the behaviour of the tumor should be considered and imaging should be repeated when tumors display aggressive or recurrent behaviour.