BACKGROUND - The purpose of this study is to establish the validity of F-18-deoxyglucose positron emission tomography-computed tomography (FDG-PET-CT) scan staging for cutaneous melanoma when a musculoskeletal image abnormality is detected.
METHODS - An institutional review board (IRB)-approved prospective database was queried to identify 342 melanoma patients treated between 4/1999 and 12/2007. A total of 682 whole-body FDG-PET-CT scans performed for staging were retrospectively reviewed to identify FDG-avid lesions in the deep soft tissues/muscle, bone or joints (i.e., musculoskeletal sites). Images were correlated with follow-up patient records.
RESULTS - There were 187 true-positive sites on 94 scans and 26 false-positive sites on 22 scans. The overall false-positive rate was 13.9% (26/187). The positive predictive value (PPV) of an isolated musculoskeletal FDG-avid site was 31%. The PPV was highest (100%) when findings were present in both the bone and deep soft tissues. The relative risk of an isolated FDG-avid site compared with multiple FDG-avid sites not being melanoma was 5.33 [95% confidence interval (CI) 2.85-9.94]. The relative risk of an FDG-avid site seen in the appendicular region not being melanoma was 1.78 (95% CI 0.87-3.64) that of a site seen in the axial region.
CONCLUSIONS - FDG-PET-CT scanning for staging and surveillance in the extremities of patients with high-risk melanoma often creates confusing clinical scenarios. Our data suggest that a select subset of patients with isolated avid appendicular musculoskeletal scan may not have metastatic melanoma.