Spinal Cord Injury - Leg Cycling

HISTORY: A 27-year-old male presented with a chronic spinal cord injury (5 years) sustained at the thoracic level (T8). PHYSICAL EXAMINATION: The participant was clinically examined using the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). He presented with total paralysis and no sensory function for hip flexors, knee extensors, ankle dorsiflexors, ankle plantarflexors and long toe extensors of both legs. According to the American Spinal Cord Injury Association, his injury was classified as complete (AIS A). DIFFERENTIAL DIAGNOSIS: We recorded the surface electromyographic (EMG) activity of sixteen lower limb muscles (eight muscles on each leg) and forces applied to the pedals during leg cycling. The individual was seated in his wheelchair and his feet were secured to the pedals of a cycle ergometer. Two examiners manually rotated the cranks at a cadence of 30 rotations per minute while the individual was instructed to volitionally contribute to the displacement of the cranks. We observed EMG bursts (i.e. changes in the activity within the pedal cycle) in all his left muscles and 5 out 8 muscles in his right limb, but no EMG bursts were identified in the knee extensors (i.e. rectus femoris, vastus lateralis and vastus medialis). The peak amplitude of the force applied to the left and right pedals equaled 89 and 73 N, respectively. TEST AND RESULTS: In an attempt to increase the spinal concentration of serotonin (5-HT) below the lesion to facilitate residual locomomotor function, the participant ingested a capsule containing 50 mg of the serotonin precursor, 5-hydroxytryptophan (5-HTP) combined with 50 mg of carbidopa. The leg cycling exercise was repeated 2.5 hours following drug administration. EMG bursts were observed in all 16 muscles with an average four-fold increase in EMG activity of the muscles (all p < 0.001) which was accompanied by larger peak forces applied to the left (+20 N; p < 0.001) and right pedals (+30 N; p < 0.001). FINAL WORKING DIAGNOSIS: Deficit in spinal concentration of serotonin. TREATMENT AND OUTCOMES: Oral administration of 5HTP facilitated excitability of the locomotor network and increased force production during leg cycling, presumably through an increase in the spinal concentration of serotonin. FUNDING: Wings For Life - Spinal Cord Research Foundation