Smudging of the Motor Cortex Is Related to the Severity of Low Back Pain

Study Design. Cross-sectional design. Objective. Here we aimed to determine whether motor cortical reorganization in low back pain (LBP) can be identified using noninvasive surface electromyographic (EMG) recordings of back muscles at different lumbar levels, and whether cortical reorganization is related to clinical features of LBP. Summary of Background Data. Reorganization of motor regions of the brain may contribute to altered motor control, pain, and disability in chronic LBP. However, data have been limited by the need for invasive recordings of back muscle myoelectric activity. The relationship between altered cortical organization and clinical features of LBP remains unclear. Methods. In 27 individuals with recurrent, nonspecific LBP and 23 pain-free controls, we mapped the motor cortical representation of the paraspinal muscles using transcranial magnetic stimulation in conjunction with noninvasive surface EMG recordings at L3 and L5 levels. Clinical measures of pain severity, location, and duration were made. Results. The results demonstrate a loss of discrete motor cortical organization of the paraspinal muscles in chronic LBP that can be identified using noninvasive EMG recordings. A loss of discrete cortical organization was clearer when surface electrodes were positioned at L3 rather than L5. A novel finding was that altered motor cortical organization (number of discrete peaks and map volume) was associated with the severity and location of LBP. Conclusion. These data suggest that surface EMG positioned at L3 is appropriate for the identification of changes in the motor cortex in LBP. Furthermore, our data have implications for treatment strategies that aim to restore cortical organization in LBP.