Diagnostic and prognostic value of compound motor action potential of lower limbs in acute paraplegic patients

Objectives: To evaluate the diagnostic and prognostic contribution of motor nerve conduction studies (NCS) in addition to neurological examination in patients with acute paraplegia. Methods: In 79 patients with acute onset of paraplegia due to traumatic or ischaemic damage of the conus medullaris/cauda equina (conus/cauda) or lesi on of the mid-thoracic spinal cord (epiconal) neurological (initial and fol low-up clinical motor and sensory scores; outcome of ambulatory capacity de termined at least 6 months post-trauma) and electrophysiological examinatio ns (motor nerve conduction velocity (MNCV) and compound motor action potent ial (CMAP) of tibial and peroneal nerves) were performed in parallel. Results: Severe axonal motor neuropathies were significantly caused by conu s/cauda lesions (loss of tibial CMAP in 71% and of peroneal CMAP in 68%) co mpared to patients with epiconal lesion (no loss of tibial CMAP and abolish ed peroneal CMAP in 14%). The CMAPs were deemed acutely pathological 4-14 d ays post-trauma and were indicative of the severity of conus/cauda lesion w hile the MNCV remained normal. Follow-up recordings (up to 1 year post trau ma) revealed no significant change in the CMAP values. The clinical examina tion according to the American Spinal Injury Association (ASIA protocol) in contrast to the CMAP values was significantly related to the outcome of am bulatory capacity. Conclusions: In contrast to patients with an epiconal SCI almost all patien ts with damage of the conus/cauda present a severe axonal neuropathy of the tibial and peroneal nerves, Pathological CMAPs develop as early as 1-2 wee ks after onset of acute paraplegia. They allow, at an early stage: to diffe rentiate between conus/cauda or epiconal lesion and to assess the severity of conus/cauda lesion. Thereafter follow-up examinations remain stable and a developing worsening of peripheral nerve or spinal cord function: eg due to post-traumatic syringomyelia, may be indicated by a secondary deteriorat ion of CMAP values. The clinical examination, according to the ASIA protoco l, in acute paraplegia patients, in contrast to the motor nerve conduction studies, is of prognostic value in predicting the outcome of ambulatory cap acity.