Duchenne muscular dystrophy (DMD) patients who are nonambulatory tend to have lower bone mineral density (BMD) scores than ambulatory patients, and DMD patients with prevalent clinical fractures also have lower BMD Z-scores, according to a new article published in the Journal of Endocrinological Investigation.

The Italian researchers found that lumbar spine BMD Z-scores were positively correlated with forced vital capacity (FVC) scores (r =.50; P =.01). In particular, nonambulatory patients had lower mean FVC scores (32 vs 91; P <.0001) but were also older in age (19 vs 8; P =.04) than ambulatory patients.

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Using stepwise multiple regression analysis, it was determined that age (P =.0034), BMI (P =.0007), FVC (P =.0006), and sclerostin levels (P =.042) were all independently associated with lumbar spine BMD Z-scores, after correcting for glucocorticoid use, 25(OH)D levels, bone turnover markers, and left ventricular ejection fraction (LVEF) measures.

“While we understand that the ambulatory status, FVC as a main indicator of respiratory function, and overall health status would deteriorate with time, it is not surprising that BMD would also worsen along the same clinical path, as part of the natural history in DMD,” the study’s authors said.

Based on the study’s results, the authors highlighted the need for multidisciplinary teams to take into account bone fragility as it could possibly lead to lower limb fractures, which could then reduce the ambulatory phase for patients.

According to the authors, the loss of ambulation could further reduce activity and lead to even more bone loss. The decreased bone density can also lead to an increase in vertebral fractures, worsened respiratory symptoms, and a reduced life expectancy, even if the patient is asymptomatic.

Relationships between several biomarkers were also investigated. The study found that osteocalcin, a biomarker for bone formation, was negatively correlated with age (r =− .6; P =0.009) and urinary calcium levels (r =− .721; P =0.03) but positively correlated with procollagen type 1 (r =.8; P =.001) and FVC (r =.55; P =.02). Urinary calcium levels were also correlated with patient age (r =.77; P =.01).

During the study, a total of 31 DMD patients were recruited, with 11 still being ambulant. Of these 31 patients, 9 reported a history of fractures whether appendicular or vertebral. BMD was measured using a bone densitometer and converted to Z-scores based on age and adjusted by height. Patients also underwent echocardiograms to determine LVEF, spirometry for FVC, and collection of venous blood and urine samples for laboratory data analysis.

Reference

Catalano A, Vita GL, Bellone F, et al. Bone health in Duchenne muscular dystrophy: clinical and biochemical correlates. J Endocrinol Invest. Published online September 15, 2021. doi:10.1007/s40618-021-01676-4