OBJECTIVE. The purpose of this study was to evaluate the use of a recently described assessment tool to quantify bone marrow response to enzyme replacement therapy in a cohort of adult patients with type 1 Gaucher's disease.MATERIALS AND METHODS. Serial MR images of the femurs, lumbar spine, or both of 57 subjects with a diagnosis of Gaucher's disease, 44 of whom were being treated with enzyme replacement therapy, were evaluated by two musculoskeletal radiologists using the bone marrow burden ( BMB) scoring system. This system gives a score out of a possible 8 for the lumbar spine and a score out of a possible 8 for the femurs, so the total BMB score is out of 16.RESULTS. The mean total BMB scores at baseline and final measurement were 13 ( 95% CI, 12.0-13.8) and 6.5 ( 95% CI, 5.2-7.9), respectively. Total BMB scores improved by 2-12 points ( mean, 6.3 points) for 15 subjects in whom total BMB scores obtained before enzyme replacement therapy and at least one time point after commencement of therapy were available. In 39 subjects for whom only baseline and final femoral BMB scores were available, 24 subjects ( 62%, 95% CI, 47-76%) improved by 2 or more points while on enzyme replacement therapy. In 24 subjects for whom only baseline and final lumbar BMB scores were available, the BMB score in 16 subjects ( 67%, 95% CI, 48-85%) improved by 2 or more points.CONCLUSION. The use of the BMB score enabled semiquantitative assessment of bone marrow response to enzyme replacement therapy in adult patients with type 1 Gaucher's disease in Australia. The ability to assess therapy response will facilitate the tailoring of dosage regimens in the future.