Intraobserver and interobserver variability of the bone marrow burden (BMB) score for the assessment of disease severity in Gaucher disease. Possible impact of reporting experience.

Aim: To evaluate the intraobserver and interobserver agreement for bone marrow burden (BMB) scores for individual examinations and for the change in BMB score over time in the same patient.

Methods: A total of 119 sets of MR images of the lumbar spine and femora from 60 patients with Gaucher disease were included. Each set of MR images was scored using the BMB score independently by two experienced MSK radiologists. One radiologist performed a second read four weeks later. Intraobserver and interobserver agreement was assessed using Bland-Altman analysis and weighted kappa scores.

Results: BMB scores (n=119) demonstrated fair intraobserver agreement (weighted kappa=0.53) with a mean difference of -0.20 and 95% limits of agreement (LOA) of (-3.41, 3.01). Inter observer agreement was poor with weighted kappa 0.28 with mean difference of -0.16 and 95% LOA of (-4.45, 4.11). Change in BMB scores over time (n=59) demonstrated poor/fair intraobserver agreement (weighted kappa 0.41, mean difference-0.20 and 95% LOA (-4.35, 3.94)). Interobserver agreement was poor (weighted kappa 0.25, mean difference -0.12 with wide 95% LOA (-6.23, 5.99)).

Conclusion: Significant interobserver, and to a lesser extent intraobserver, variation occurs with blinded BMB scoring of Gaucher disease.