Comparison of conventional magnetic resonance imaging and diffusion-weighted imaging in the differentiation of bone plasmacytoma from bone metastasis in the extremities

•On conventional magnetic resonance imaging bone plasmacytoma and bone metastasis in the extremities display different morphological patterns.•Apparent diffusion coefficient (ADC) and standard deviation of ADC derived from diffusion-weighted imaging show the highest AUC in differentiating between plasmacytoma and metastasis in the extremities.•The addition of diffusion-weighted imaging to conventional MRI improves the capabilities of MRI to discriminate between plasmacytoma and bone metastasis in the extremities. To compare conventional magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) in the differentiation of bone plasmacytoma from bone metastasis in the extremities. A total of 65 patients with 27 bone plasmacytomas (11 men; mean age, 63.6±8.2 [SD] years) and 38 patients with bone metastases (20 men; mean age, 64.1±11.5 [SD] years) were retrospectively included. Plasmacytomas and metastases were compared for size, peritumoral edema, signal intensity (SI), SI pattern, apparent diffusion coefficient (ADC) values and standard deviation (SD) of ADC. Receiver operating characteristic analysis with area under the curve (AUC) was used to calculate sensitivity, specificity, and accuracy of MRI and DWI for the diagnosis of plasmacytoma according to a defined cut-off value. On conventional MRI, plasmacytomas showed less peritumoral edema (22% vs. 71%; P