Bone Abstracts

Objective: A retrospective review of bone morbidity in a contemporary cohort of boys with Duchenne muscular dystrophy (DMD) currently managed in a Scottish tertiary neuromuscular centre.

Method: Clinical details and results of bone surveillance were obtained in 47 boys, aged 9 years (2–16). DXA bone mineral content (BMC) at total body (TB) and lumbar spine (LS) were adjusted for bone area. Fractures were classified based on radiological confirmation. Results are reported in median (range).

Result: At last follow-up, 39/47(82%) were on steroid therapy and 26 (55%) were ambulant. 5/10 (50%) of those over 14 had delayed puberty and all of these boys had testosterone therapy. All were treated with oral vitamin D (800–1000 units per day) and of 35 who had Vitamin D measured, 5 (14%) had a level<25 nmol/l. 12 boys (26%) had sustained a total of 15 symptomatic fracture events. Of these 15, 12 (80%) were appendicular fractures (AF) and 3(20%) were vertebral fractures (VF). AF occurred at a median age of 6 years (2.5, 14) in 9 boys. The distribution of these 12 AF was 7 (58%) tibia/fibula, 3 (25%) femur and 2 (17%) humerus/radius/ulna. Mechanisms of injuries were 11 (92%) minor fall and 1(8%) while being lifted. Median length of steroid exposure was 4 years (0, 10). 7/9 boys (75%) were ambulant prior to fracture. 2/11 (18%) lost ambulation after fracture. 3/12 (21%) of AF (femoral, tibia, fibula) occurred in two boys under 3 years who were steroid naïve and ambulant. DXA and vitamin D level within 1 year of AF were available in 10/12 fracture episodes. Median TB BMC SDS was 0.1(−0.8, 1.0) and LS BMC SDS was −0.2 (−1.2, 1.0). Vitamin D level was <25 nmol/l in 2/10 (20%). VF occurred at a median age of 11 years (9, 13) in three boys. 2/3 boys were ambulant. Median length of steroid exposure was 6 years (5, 8). DXA within 1 year of VF showed TB BMC SDS 0.3 (−0.2, 1.1) and LS BMC SDS −0.1 (−0.6,0.8). None had vitamin D <25 nmol/l.

Conclusion: In boys with DMD, symptomatic VF occur in older children, with longer duration of steroid therapy. AF occurs in younger boys and can also present in very young, ambulant, steroid naïve boys. Coincidental severe vitamin D deficiency or reduced BMC were not common findings at a fracture event.

Disclosure: The authors declared no competing interests.