FDG-PET/CT Is Superior to Anatomic Imaging for the Staging and Follow Up of Bony Involvement in Patients with Lymphoma.

Background and Objectives: Positron tomission tomography using 18fluoro-2-deoxyglucose in combination with low dose non-enhanced computed tomography (FDG-PET/CT) is increasingly utilized in the management of patients with lymphoma. Numerous studies have demonstrated improved accuracy for both staging and restaging as compared to standard diagnostic CT. However, there is a paucity of data on the significance of bone uptake in patients with lymphoma. This is one area in which FDG-PET has the potential to dramatically influence care of lymphoma patients. However, false positive FDG-PET has been shown in patients with traumatic or benign bone lesions. The aim of this study was to evaluate the utility and accuracy of FDG-PET/CT in comparison with standard anatomic imaging with CT and MRI in the staging and follow up of patients with Hodgkin lymphoma (HL) or diffuse large B cell lymphoma (DLBCL).

Design and Methods: We reviewed a database of 75 lymphoma patients who underwent concurrent FDG-PET/CT and standard diagnostic CT scans or MRI, and identified those with bone involvement by lymphoma. Involvement of bone was demonstrated by either biopsy of a bone lesion or radiologic appearance and clinical follow up highly suggestive of bone involvement. Follow up studies were evaluated for resolution of FDG avid lesions on PET, and anatomic lesions on CT or MRI.

Results: Fourteen patients with either HL or DLBCL who underwent both FDG-PET/CT and diagnostic CT were identified to have bone involvement by lymphoma. FDG-PET identified bone involvement in all 14 patients, whereas CT imaging identified bone involvement in seven. One patient in whom CT did not detect bone involvement had evidence of bone lymphoma by MRI. Eight patients had confirmation of bone lymphoma by biopsy, while 6 were confirmed by clinical criteria (radiologic appearance and clinical follow up). Thirteen of the patients had follow up FDG-PET/CT scans, and 12 had follow up CT and/or MRI. All follow up FDG-PET scans showed resolution of FDG avid bone lesions after anti-lymphoma therapy. In contrast, all CT and MRI scans which originally showed evidence of bone involvement had persistent abnormality on follow up, with only 2 showing improvement. At a median follow up of 9 months (range 0–20 months), 11 patients remain in remission, while 2 patients subsequently showed progression by FDG-PET, CT and biopsy in soft tissue sites, but not bone. One patient remains on therapy. No patient in our series was found to have a benign etiology of a lesion initially thought due to lymphoma.

Conclusion: FDG-PET/CT is useful in the staging and follow up of patients with lymphoma with bone involvement. The lack of sensitivity of CT combined with the delayed resolution of anatomic abnormalities limit the utility of standard anatomic imaging, making FDG-PET/CT the imaging modality of choice for patients with bone lymphoma.