Can FDG PET/CT replace Bone densitometry (DXA) for detection of bone loss in adult lymphoma patients?

Objectives: Significant bone loss as measured by DXA (dual-energy x-ray absorptiometry) was recently reported in non-hodgkin lymphoma (NHL) and hodgkin lymphoma (HD) patients. Recognition of bone loss in these patients may warrant prophylactic measures and life style changes before, during and after therapy. As FDG PET/CT is part of the routine evaluation for lymphomas, this study was undertaken to assess whether FDG PET/CT could replace DXA for bone loss evaluation in these patients.

Methods: This was a retrospective, single center comparative study of bone loss in lymphoma patients as measured by PET and DXA. All patients had DXA results from a previous study and had undergone FDG PET/CT within 6 months of DXA. Patients were included if they did not have bone marrow involvement, if bone uptake on PET was normal and no bone lesions were detected on CT in the lumbar spine and femoral neck. SUVmax and SUVmean measured in L1-L4 (as an average) and in the femoral neck were compared with corresponding bone mineral density (BMD) values on DXA. The study evaluated: a. the correlation between SUV and BMD values, b. the performance of SUV threshold values for predicting bone loss and c. its relation to various clinical parameters.

Results: Thirty-two lymphoma patients (NHL 25, HD 7) were included. The mean age was 60y (range: 25-90), 14 were male, 8 were prior to treatment and 24 were treated. Twenty (62%) patients had bone loss (osteopenia 12, osteoporosis 8) and 12 normal bone density as measured by DXA. A significant positive correlation was found between average lumbar SUVmax or SUVmean and the corresponding lumbar BMD (p<0.006 for SUVmax, p<0.009 for SUVmean) and T scores (p<0.01 for both SUVmax and SUVmean). A significant positive correlation was also found between femoral neck SUVmax or SUVmean and the corresponding femoral neck BMD (p<0.02 for SUVmax, p<0.05 for SUVmean) and T scores (p<0.01 for SUVmax, p<0.02 for SUVmean). There was a significant difference of the average total lumbar SUVmax or SUVmean between the 12 patients with normal BMD (SUVmax: 3.49±0.83, SUVmean: 2.41±0.52) as compared with the 20 patients with osteopenia/osteoporosis (SUVmax: 2.78±0.60, p<0.009, SUVmean: 1.99±0.45, p<0.025). ROC curve analysis defined a SUVmax of 3.0 and SUVmean of 2.4 as providing FDG PET/CT sensitivity of 70% and 85% and specificity of 66% and 58%, respectively, for predicting bone loss (osteopenia/osteoporosis). There was no significant difference in the relationships between SUV and BMD for the clinical parameters analyzed including gender, age, type and stage of lymphoma, type of therapy and time from diagnosis.

Conclusions: FDG uptake in the lumbar spine and femoral neck as measured by SUVmean and SUVmax is significantly lower in lymphoma patients with bone loss than those with normal BMD on DXA. Lumbar SUVmax and SUVmean threshold values of 3 and 2.4, respectively, predict decreased bone density with an acceptable sensitivity and specificity. Routine FDG PET/CT in lymphoma patients can potentially detect bone loss and may indicate the need for preventive measures in these patients. These results need to be substantiated in studies with larger number of patients.