Relationship between electromyography and computed tomography in the evaluation of low back pain

In a group of 109 patients with low back pain, the electromyographic(EMG) findings were compared with computed tomographic (CT) findings. There were 64 (58.7%) patients who had abnormal EMG results combined with abnormal CT findings. 11 (10.1%) cases had abnormal EMG and normal CT findings, another 11 (10.1%) patients had abnormal CT and normal EMG findings. 33 patients underwent operation; nerve root compressions were confirmed in all those with abnormal EMG findings, and 32 of those with abnormal CT findings. Among 33 surgical cases, 24 (72.7%) patients had abnormal EMG findings in both paralumbar and lower extremity muscles. In 9 (27.3%) patients there was evidence of abnormal EMG findings in the paralumbar muscles only. Among 46 who had abnormal EMG findings in paralumbar and lower limb muscles, 44 (95.6%) patients had combined CT abnormalities, and in the remaining 2 patients, nerve root 'compression was confirmed by surgery in 1 case and by myelogram in the other. In 29 cases with abnormal EMG findings in the paralumbar muscles only, 20 (69.0%) patients had combined CT abnormalities. In comparing normal versus abnormal EMG findings of the paralumbar muscles only, a significantly higher percentage of abnormal CT results were found among the abnormal EMG findings. These results indicate that abnormal EMG findings in both the paralumbar and lower limb muscles, strongly suggests the presence of nerve root compression. In cases where there are abnormal EMG findings in the paralumbar muscles only, it is recommended that CT scan must be done for the correct diagnosis of low back pain.