Lack of clinically meaningful anatomical variations in bone marrow apparent diffusion coefficient in diffuse pattern myeloma allows untargeted sampling to confirm disease burden

Abstract

Posterior iliac crest trephine may result in sampling error and incorrect measures of disease burden in patients with multiple myeloma. This may influence the decision to treat. To compare the regional apparent diffusion coefficient of bone marrow in patients with multiple myeloma without focal bone lesions and their correlation with indices of disease burden, whole-body diffusion weighted imaging of 48 patients with diffuse myeloma were retrospectively reviewed. Three regions of interest were drawn over four anatomical sites on apparent diffusion coefficient maps and average values recorded. Apparent diffusion coefficient values were compared using the Wilcoxon signed-rank test with p-value < 0.0125 (Bonferroni correction) taken as statistical significance. Average apparent diffusion coefficient values were correlated with age-adjusted marrow cellularity and plasma cell proportion at histopathology, and international staging system scores. There was no significant difference in the apparent diffusion coefficient of bone marrow in the left ilium (754 × 10 -6 mm 2 /s), right ilium (733 × 10 -6 mm 2 /s) and T6 (701 × 10 -6 mm 2 /s) but it was significantly lower in L3 (636 × 10 -6 mm 2 /s) (p-value < 0.0125). However, the variance of apparent diffusion coefficient across all sites were within limits of measurement repeatability (15%). No correlation was found between per-patient average apparent diffusion coefficient with age-adjusted marrow cellularity (p=0.7), proportion of plasma cells (p=0.2) or ISS scores (p=0.5). There was no clinically meaningful difference in apparent diffusion coefficient values across anatomical sites in diffuse myeloma. Untargeted bone marrow biopsy is likely to be representative in this patient group.