Cortical Reorganization Following Neurotization: A Diffusion Tensor Imaging and Functional Magnetic Resonance Imaging Study

BACKGROUND: Following successful intercostal-musculocutaneous nerve (ICN-MCN) neurotization for brachial plexus injuries (BPIs), patients initially show a synkinetic movement of elbow flexion during inspiration. Later they are able to flex the elbow, independent of respiratory activity. OBJECTIVE: To demonstrate cortical reorganization following ICN-MCN coaptation in BPI through functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). METHODS: Thirty adult patients underwent ICN-MCN coaptation for BPI. The controls were age and sex matched. All patients had Sunderland 3 or 4 degree of injury. Patients underwent fMRI and DTI (pre- and postoperatively) with electromyography of the biceps. Maps of neural activity within the motor cortex were generated in the paralyzed and control arms and center of maximum activity was calculated. Fractional anisotropy and apparent diffusion coefficient were generated from fMRI and DTI over the motor cortex and comparison was made between the paralyzed and control arms. RESULTS: Median deinnervation interval was 6 months. Seventeen patients improved from grade 0 to grade 3 or more. There was no significant difference between the coordinates for maximum activity, when the cortical activity following elbow flexion of the patients who improved was compared with the control arm activity. There was reduction in FA and ADC values in patients who have improved following surgery when compared to controls. Fractional anisotropy and apparent diffusion coefficient values of the postoperative patients revealed no significant difference from the controls or preoperative patients. CONCLUSION: Cortical plasticity following ICN-MCN transfer in BPI does occur. There was no correlation between the degree of improvement either with the transposition of activity on the motor cortex from the chest to the elbow area, or the amount of activity on the motor cortex representing the elbow area.