99mTc-Sestamibi Scintigraphy to Monitor the Long-Term Efficacy of Enzyme Replacement Therapy on Bone Marrow Infiltration in Patients with Gaucher Disease

Assessing the skeletal response to enzyme replacement therapy (ERT) in Gaucher disease (GD) is problematic. We investigated the reliability of 99mTc-sestamibi scintigraphy in monitoring changes in bone marrow involvement induced by ERT. Methods: In 52 GD patients, the efficacy of ERT on bone marrow disease was monitored using at least 2 sequential 99mTc-sestamibi scans; 17 patients were receiving ERT at enrollment, and 35 were ERT-naïve. We elaborated a dose–response model by statistical analysis based on linear mixed models. Results: Patients whose marrow disease improved had received a significantly higher ERT dose per month than patients who did not improve. Significantly more patients reached near-disappearance of marrow disease if their disease burden at enrollment had been lower and the duration of clinical signs shorter. The response of the marrow scintigraphic score was more pronounced in ERT-naïve patients. No relevant effect of ERT on marrow disease was observed until platelet count and splenomegaly had improved. Conclusion: Although based on localized evaluation, changes in the 99mTc-sestamibi score closely correlated with the main determinants of ERT, with a definite dose–response relationship. The threshold at which ERT induced any improvement in bone marrow disease was 35–36 U/kg/mo; in ERT-naïve patients, the scintigraphic score declined by 1 unit after ERT at 28 U/kg/mo.