Background: In Duchenne Muscular Dystrophy (DMD), osteoporosis results in long-bone and vertebral fractures (VFs), which are not adequately predicted by bone mineral density measured using dual-energy X-ray absorptiometry (DXA). Increased bone marrow fat fraction (FF) has been reported in multiple bone fragility populations. We hypothesize that MRI measurement of bone marrow fat fraction of vertebral and long bones may provide valuable additional information about bone health in DMD.
Methods: 12 boys with DMD (12.6 ± 3.1 years; duration of corticosteroid exposure= 6.8 ± 3.3y) and 7 unaffected boys (n= 7; age=13.0 ± 3.3y) participated in this ongoing observational study. A 3T whole body MRI scanner is used to obtain bone marrow FF of L4 vertebral body, mid femur, and distal femur for both groups using magnetic resonance spectroscopy in the spine and chemical shift encoded MRI in the femur.
Results: Bone marrow fat fraction was significantly elevated in the L4 vertebra, (DMD: mean ± SD; 0.57± 0.19; unaffected: 0.26± 0.12, P=0.01), and distal femur (affected: 0.90± 0.04; unaffected: 0.78± 0.07, P=0.0007). At the mid femur, a trend for higher FF in DMD was seen (affected: 0.84± 0.11; unaffected: 0.74± 0.07, P=0.06). In the spine and distal femur of boys with DMD, bone marrow fat fraction was significantly correlated with age (spine: r=0.57, femur: r=0.73) and duration of glucocorticoid exposure (spine: r
=0.83, femur: r=0.66)). Vastus lateralis muscle fat fraction, which increases with disease progression and correlates closely with function in DMD, was correlated with femur bone marrow fat fraction ( r=0.46) but not spine bone marrow fat fraction.
Conclusion: Bone marrow fat fraction captures alterations in bone quality with age and disease progression at the spine and distal femur in boys with DMD.