Role of FDG-PET/CT in Extramedullary Multiple Myeloma: Correlation of FDG-PET/CT Findings With Clinical Outcome.

Purpose: The aim of this study was to describe FDG-PET/CT findings in extramedullary multiple myeloma (EMM) correlating them with clinical outcome.

Methods: In this institutional review board-approved HIPAA-compliant retrospective study, we reviewed the FDG-PET/CT scans of 35 patients with EMM (16 women, 19 men; mean age, 56 years; median follow-up after the diagnosis of EMM, 14 months) out of 156 patients diagnosed with MM at our institute between 2004 and 2012. The distribution and metabolic activity of EMM on the scans were reviewed. Clinical data were extracted from electronic medical records. Statistical analysis was performed to determine differences in outcome based on time of detection and distribution of EMM.

Results: Extramedullary multiple myeloma was present at diagnosis in 12 of 35 patients and during disease progression in 23 of 35 patients. Indications for FDG-PET/CT were initial staging (12/35), restaging for disease progression (18/23), or assessment of response to therapy (5/23). Extramedullary multiple myeloma was FDG-avid (mean SUVmax, 8.4; range, 1.2-31), solitary in 10 patients (29%) and multifocal in 25 patients (71%). Two patterns of distribution were noted: direct extension of osseous plasmacytomas in 18 (51%) of 35 patients and hematogeneous/lymphangiogenic dissemination in 33 (94%) of 35 patients. Mean SUVmax in lesions with direct osseous extension was statistically higher than hematogeneous/lymphangiogenic EMM (Mann-Whitney U test, P = 0.03). The most common sites of hematogeneous/lymphangiogenic spread of EMM were lymph nodes (21/35 [60%]), liver (10/35 [29%]), lung (9/35 [26%]), muscles away from bones (7/35 [20%]), and peritoneum/mesentery (7/35 [20%]). There was no statistically significant difference in distribution of EMM at presentation and during disease progression (χ2 test, P > 0.05); 24 (69%) of 35 patients died (median interval after diagnosis of EMM, 7 months). There was no statistically significant difference in outcome for EMM at presentation and during disease progression (log-rank test, P = 0.068). Involvement of any of the following 3 sites: liver, lung, and muscles away from bones, was associated with statistically significant shorter survival (log-rank test, P = 0.0008).

Conclusions: Extramedullary multiple myeloma is more often seen on FDG-PET/CT in the context of a hematogeneous/lymphangiogenic spread pattern and less commonly as a direct extension of osseous plasmacytomas. Extramedullary multiple myeloma has poor outcome whether detected at presentation or during follow-up. Extramedullary multiple myeloma involving the liver, lung, and muscles was associated with shorter survival in our study.