Is Bone Health Monitored Enough in Duchenne Muscular Dystrophy?

Sze Choong Wong, MD, from the Developmental Endocrinology Research Group, Royal Hospital for Children, in Glasgow, United Kingdom

Sze Choong Wong, MD

Findings from a recently published study suggest that bone health and fracture monitoring in boys with Duchenne muscular dystrophy (DMD) should be conducted regularly, as results showed a high incidence of radiologically confirmed fractures among a national cohort.

Notably, the investigators, led by Sze Choong Wong, MD, from the Developmental Endocrinology Research Group, Royal Hospital for Children, in Glasgow, United Kingdom, suggested that the 48% rate of confirmed symptomatic fractures was “likely to be a gross underestimation of the real frequency in this population.” Most of the fractures occurred in the femur (33%) and the tibia (30%).

“Bone monitoring in this national cohort is inconsistent and should now include routine imaging of the spine with lateral thoracolumbar spine x-rays,” they wrote.

The Scotland-based study included 91 boys with DMD with a mean age of 11.3 years, of which 51% (n = 46) were non-ambulant. In total, 59 patients (65%) had been on a glucocorticoid treatment regimen, and an additional 23 (25%) had been exposed to glucocorticoid treatment. The majority of those who discontinued treatment (n = 17) did so because of the loss of ambulation.

In total, 44 patients had sustained 51 fractures, with 5 patients experiencing multiple fractures. Non-vertebral fractures were the most common (43), occurring in 36 patients (40%), though symptomatic vertebral fractures occurred in 7 patients (8%) and both occurred in a single patient. Non-vertebral fracture episodes occurred predominantly in the lower limb, at a rate of 72% (n = 31).

Plasma 25 hydroxy-vitamin D levels were measured in 51% of patients (n = 46) in the previous 12 months, and median vitamin D levels were 49 nmol/L. Dual-energy x-ray absorptiometry (DXA) assessments were conducted at least once in 63 patients (69%), with those currently on glucocorticoid therapy more likely to have had an assessment (n = 37; 63%) compared with those who were glucocorticoid-naïve (n = 8; 29%).

“The complex interplay between underlying muscle weakness and [glucocorticoid] therapy, together with other factors that may impact on bone health and therefore fracture risk in DMD needs to be teased out in well-designed research studies,” Wong and colleagues wrote. “Routine imaging with lateral thoracolumbar spine x-rays should be incorporated into such studies, and indeed in clinical monitoring of these boys.”

The investigators added that it was worth acknowledging that their cohort was younger in terms of age at loss of ambulation, though juxtaposed to recent findings, increased fracture incidence at the time of ambulation loss was not observed.²

They also pointed out that while delayed puberty is common—present in about 80% of older adolescents undergoing clinical assessment of puberty following referral to pediatric endocrinology in this review—puberty was only documented in half of the cohort. Therefore, the prevalence of delayed puberty in those treated with glucocorticoid therapy is currently still unknown.

“Emerging evidence suggests that these boys have persistent hypogonadism and may, therefore, have long-term consequences to the skeleton even in adulthood,” they added. And though testosterone can lead to increased bone mass, there are limited studies on the effects of testosterone on skeletal development and growth in boys with DMD. “But this deserves greater attention,” they noted.

“Routine pubertal assessment in these boys should be given attention in the neuromuscular clinics with timely referral to pediatric endocrinology for management of puberty,” Wong and colleagues wrote. “Multicenter prospective studies are required to clearly understand the determinants of asymptomatic as well as symptomatic fractures in this at-risk group.”

REFERENCES

1. Joseph S, Qang C, Di Marco M, et al. Fractures and bone health monitoring in boys with Duchenne muscular dystrophy managed within the Scottish Muscle Network. Neuromuscular Disord. 2019;29(1):59-66. doi:10.1016/j.nmd.2018.09.005

2. Perera N, Sampaio H, Woodhead H, Farrar M. Fracture in Duchenne muscular dystrophy: natural history and vitamin d deficiency. J Child Neurol. 2016;31(9):1181-7. doi: 10.1177/0883073816650034.