Increased 18F-FDG uptake in degenerative disease of the spine:: Characterization with 18F-FDG PET/CT

We determined the prevalence of abnormal spinal F-18-FDG uptake and assessed the relationship between the severity of findings on F-18-FDG PET and the severity of degenerative spinal disease (DSD) on CT. Methods: PET/CT scans of 150 patients > 18 y old, referred for whole-body F-18-FDG PET/CT for evaluation of known or suspected malignancy from June to July 2002, were analyzed retrospectively for the presence of increased F-18-FDG uptake in the spine and for anatomic correlates. Initially, PET images were examined and foci of F-18-FDG uptake in the spine were graded on a 0-4 scale based on intensity of F-18-FDG uptake (0 = definitely normal, 1 probably normal, 2 equivocal, 3 = probably abnormal, 4 definitely abnormal). From PET alone, an impression as to whether lesions were most likely metastases or degenerative, as well the level of the spine involved, was also recorded. CT images of all 150 patients were reviewed independently by a musculoskeletal radiologist, who was unaware of patient identification, history, and findings of other imaging modalities, with the location recorded and severity graded on a 4-point-scale (0 = normal, 1 = mild, 2 = moderate, 3 = severe for both degenerative disk and facet disease). The relationship between PET and CT findings was then determined. Results: Of the 150 patients, 63 (42.0%) had no abnormal findings in the spine on PET (grade 0), 27 (18.0%) had grade 1, 25 (16.7%) had grade 2, 17 (11.3%) had grade 3, and 16 patients (10.7%) had grade 4 F-18-FDG uptake for DSD. Two additional patients had apparent spinal metastases with no degenerative changes. Five patients had metastases and DSD (included above). Of the patients who had abnormal spinal findings graded as probable or definite for DSD on CT (grades 3-4), 11 had abnormal findings in the cervical spine, 16 in the thoracic spine, and 23 patients in the lumbosacral spine. Seven patients (4.7%) had PET findings suggestive of spinal metastases. For patients with a maximum regional DSD score of 3, the mean F-18-FDG uptake for that spinal level was 1.4 +/- 1.5, whereas for patients with a maximum regional DSD score of 0, the mean PET grade was significantly lower at 0.4 +/- 0.9 (P = 0.0001). Conclusion: Incidental findings on PET suggestive of DSD are common (22% of patients), most common in the lumbosacral spine, and can be recognized on CT. The severity of PET findings correlates with the severity of degenerative disk and facet disease as graded by CT, likely due to the fact that the inflammatory process that accompanies DSD is evident on PET. Increased F-18-FDG uptake in DSD should not be confused with metastatic disease.