From spinal shock to spasticity - Neuronal adaptations to a spinal cord injury

Objective: To investigate the adaptational changes in excitability of spina l neuronal circuits below the level of lesion from spinal shock to spastici ty in patients with spinal cord injury (SCI). Methods: More than 6 months a fter an acute SCI, clinical, follow-up examinations were paralleled by elec trophysiologic recordings with tibial nerve stimulation (M-wave, F-wave, H- reflex, and flexor reflex). Results: During spinal shock, the loss of tendo n tap reflexes and flaccid muscle tone were associated with low persistence of F-waves and loss of flexor reflexes, whereas H-reflexes were already el icitable. During the transition to spasticity, the reappearance of tendon t ap reflexes and muscle tone and the occurrence of spasms was associated wit h the recovery of F-waves and flexor reflex excitability, whereas the H-to- M ratio remained about stable over months. At later stages (2 to 6 months a fter SCI) when clinical signs of spasticity became established, the electro physiologic measures showed little change. In paraplegic patients, in contr ast to tetraplegic patients, M-wave and flexor reflex amplitudes even decre ased. Conclusions: The late decrease in M-wave and flexor reflex amplitude in paraplegic patients suggests a secondary impairment/degeneration of prem otoneuronal circuits and of motoneurons. The divergent course of clinical s igns of spasticity and their probable neuronal correlates indicates the occ urrence of nonneuronal changes contributing to spasticity.