The most reliable method for diagnosis of injury to the brachial plexus remains intra operative exploration. Electrodiagnostic tests primarily rely on the afferent sensory pathway. It has always been assumed that the ventral and dorsal roots are usually damaged together, although the ventral roots may be more susceptible to traction. This creates false positive or false negative results with the use of somatosensory evoked potentials. This article deals with the measurement of choline acetyltransferase activity in injured spinal roots to achieve a more accurate diagnosis. Nineteen patients were included in this study. All patients had traumatic injuries to the brachial plexus. Lower plexus roots with clinical evidence of pre-ganglionic injury and pseudomeningocele formation were not examined. Eighteen C5 and seven C6 roots were explored and prepared for measurement of evoked spinal cord potentials and choline acetyltransferase activity. The evoked spinal cord potentials were measured via stimulation of the root stump and recording from a catheter placed in the posterior cervical epidural space. Choline acetyltransferase activity was measured using previously described methods. This technique required 60 minutes from resection of the nerve slices to determination of final results. Interestingly, contralateral C7 transfers have been used for the determination of normal choline acetyltransferase activity and evoked spinal cord potentials.
The injured nerve segments were divided into repairable or unrepairable categories. Repairable implies a good response during stimulation of evoked spinal cord potentials. Choline acetyltransferase activity above 2000 cpm (counts per minute) were also considered repairable. The results from this study found 15 injured roots that were deemed unrepairable and ten suitable for repair. The repairable roots were coapted to target tissue via nerve grafts. Re-enervation was assessed using needle electromyograms within four to six months. The eventual outcome is hard to discriminate because of the complexities of nerve regeneration unless some electromyographic evidence of re-enervation was present in all target muscles.
The authors conclude that the combination of evoked spinal cord potentials and choline acetyltransferase activity may be useful for decision-making in brachial plexus injuries. Evoked spinal cord potential should be used as the initial screening tool. Adequate amplitude of response indicates a repairable lesion. Failure to attain a response then requires choline acetyltransferase activity to see whether or not the root is deemed repairable. These techniques are complimentary and may provide for a more accurate and useful reconstruction. Although this technique has promise, considerable work is necessary prior to implementation in routine clinical practice.
J Bone Joint Surg