Longitudinal monitoring of apparent diffusion coefficient (ADC) in myeloma patients with lower M-gradient levels undergoing systemic treatment and whole-body MRI monitoring.

Objectives: Longitudinal assessment of changes in apparent diffusion coefficient (ADC)-values in multiple myeloma (MM) patients and their potential role for classifying disease activity.

Methods: Retrospective analysis of whole-body-MRI data in 73 stage III MM patients undergoing systemic treatment. Bone marrow involvement was evaluated using a standardized unenhanced 4-sequences whole-body-MRI protocol. We measured ADC-values in focal lesions (FL) and diffusely involved bone marrow (DIBM) areas. Response to treatment was based on the course of hematologic parameters. The time points of MRI-examinations were baseline, 1st (mean, 3 months), 2nd (mean, 10 months), and 3rd (mean, 18 months) follow up (FU).

Results: Mean IgG and IgA serum values at baseline were 2.1 mg/dl and 1.8 mg/dl, respectively. Patients were classified into responders (n = 59) and non-responders (n = 34). Some patients were re-enrolled for new treatment regimens as they became therapy-refractory. Patterns of medullary involvement were focal (n = 44), diffuse (n = 61) and mixed (n = 30). In FL, a subgroup of myeloma patients undergoing short-term 1st FU experienced a significant increase in ADC in responders (p = 0.001), but not in non-responders (p = 0.9). In the further course of the study, ADC levels decreased continuously in responders (p = 0.02) and increased slightly in non-responders (p = 0.8). In patients with DIBM, ADC values decreased in the responders (p < 0.001) and in the non-responders (p = 0.78). An ADC cut-off value of 0.5-0.6 × 10  mm/s for diagnosing inactive disease at follow-up proved unreliable.

Conclusions: In myeloma-patients with lower tumor burden, the longitudinal course of ADC-values is predictable only for FL whereas for DIBM ADC-changes considerably overlap between responders and non-responders and are not indicative for assessment of the disease activity.