Method
MRI images were reviewed from thirty two patients who were diagnosed electrodiagnostically as unilateral S1 radiculopathy. Areas of herniated disc and spinal canal were measured and the ratio of disc herniation was calculated from the axial images stored and analyzed by PACS. The radiologic measurements were compared with the results of electrodiagnostic studies.

Results
The presence of abnormal spontaneous activities in needle EMG and no response in H reflex were associated with larger disc herniation (p＜0.05). There was no other single electrodiagnostic study that showed correlation with any of radiologic measurements. With increasing number of abnormal electrodiagnostic tests, area of disc herniation grew larger (p＜0.05). Area of spinal canal and the ratio of disc herniation did not show difference between normal and abnormal groups in most of electrodiagnostic studies.

Conclusion
There were limited correlations between electrodiagnostic results and severity of disc herniation. The size of disc herniation, regardless of the size of spinal canal, was associated with abnormal results of electrodiagnostic tests. (J Korean Acad Rehab Med 2008; 32: 194-199)