FDG Positron Emission Tomography for Differentiation of Degenerative and Infectious Endplate Abnormalities in the Lumbar Spine Detected on MR Imaging

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Abstract
OBJECTIVE. The objective of our study was to evaluate the usefulness of FDG positron emission tomography (PET) for the differentiation of degenerative and infectious endplate abnormalities in the lumbar spine that were detected on MR imaging. SUBJECTS AND METHODS. FDG PET was performed prospectively in 30 consecutive patients with substantial endplate abnormalities (craniocaudal diameter of bone marrow abnormalities, ≥ 25% of vertebral height) found during MR imaging of the lumbar spine. Both the MR and PET images were evaluated by two experienced musculoskeletal radiologists and two experienced nuclear physicians. The diagnosis of either degeneration with different types of endplate abnormalities or disk-space infection was determined. Clinical follow-up and, in selected cases, bone biopsies with cultures were used as the standard of reference. RESULTS. On the MR images, 25 of the 38 degenerated levels were classified as Modic type I, 13 levels as type II, and none as type III. Five disk-space infections were diagnosed in four patients. MR imaging findings were false-positive at one disk level with type I abnormalities and false-negative at two levels with infection. PET did not show FDG uptake in the intervertebral spaces of any patient with degenerative disease. FDG PET findings were true-positive in all five levels with disk-space infection. The sensitivity and specificity for MR imaging in detecting disk-space infection were 50% and 96%, and were 100% and 100% for FDG PET, respectively (not significant, McNemar test, p = 0.5). CONCLUSION. Our findings suggest that FDG PET may prove useful for differentiation of degenerative and infectious endplate abnormalities detected on MR imaging. Even in active (Modic type I) degenerative endplate abnormalities in our series, PET did not show increased FDG uptake.