The role of PET-CT in assessment of bone marrow involvement in patients with follicular lymphoma

Objectives Involvement of bone marrow (BM) is a common feature of Follicular Lymphoma (FL) and is an adverse prognostic factor, routinely assessed by an arbitrary biopsy at the iliac crest. This study was aimed to assess the role of FDG PET-CT in identifying BM involvement.

Methods 71 patients with FL were enrolled. Visual assessment of BM uptake was categorized as normal, diffuse or focal increased uptake. Quantitative FDG uptake was measured using mean standardized uptake value (BM-SUV). Gold standard of BM involvement was based on biopsy and/or clinical and imaging follow-up

Results 21 patients (29.6%) had BM involvement. Biopsy proven in 17 (24%) and 4 (5.6%) with negative iliac crest biopsy, but increased uptake in other skeletal sites that normalized after successful therapy. BM involvement appeared visually as diffuse increased uptake in 9 (42.9%), focal in 11 (52.4%), and was falsely normal in a single case. However, diffuse uptake was seen in 18 false positive cases. Visual assessment for BM involvement had a positive predictive value (PPV) of 51% and a negative predictive value (NPV) of 97%. BM-SUV was significantly higher in patients with involvement (4.1±1.9 vs. 1.4±0.5, p<0.0001). BM-SUV greater than 2.51 had PPV of 100% for involvement with sensitivity of 86%. BM-SUV lower than 1.7 had NPV of 97.5% with specificity of 74%, for excluding involvement. Patients with involved BM per PET-CT had a mean survival of 85.5 months vs. 104.0 months in patients with no BM involvement (p=0.001).

Conclusions visual assessment of FDG PET-CT is associated with a high FP rate but is appropriate for ruling out BM involvement in patients with FL. Measurement of BM-SUV improves diagnostic accuracy. This approach identifies 25% more patients with involvement that would have been missed by iliac crest biopsy.