Sarcopenia in long-term survivors of cancer in childhood and adolescence: A cross-sectional study of calf muscle mass by peripheral quantitative computed tomography with an examination of the muscle-bone unit.

Background: Sarcopenia, a loss of systemic skeletal muscle mass (SMM), is prevalent in childhood cancer survivors and often accompanied by increased fat mass (sarcopenic obesity [SO]). We examined whether calf muscle cross-sectional area (CSA), measured by peripheral quantitative computed tomography (pQCT), can identify sarcopenia and SO in long-term survivors of pediatric acute lymphoblastic leukemia (ALL), and explored its relationship with adjacent bone geometry.

Procedures: Calf muscle CSA and CSA Z scores at the 38% tibia in 70 subjects (median survival 15 years) were compared between sexes and ALL risk group, and their association with sarcopenia and SO evaluated. Relationships between bone strength and muscle mass were assessed further using linear regression and methods described by Schoenau et al. for evaluation of a functional muscle-bone unit.

Results: A calf muscle CSA Z score of less than or equal to zero is 73.81% sensitive and 84.62% specific for detecting sarcopenia defined by height-adjusted appendicular lean mass measured by dual-energy x-ray absorptiometry. No significant difference in CSA Z scores was noted between sexes or ALL risk groups; however, Z scores were markedly higher in those without SO (adjusted odds ratio 0.529, 95% confidence interval [CI]: 0.340-0.824). Ratios of calf muscle mass to height and total bone mineral content at the 38% tibia are "sufficient" and consistent with estimated reference ranges for a healthy population.

Conclusions: CSA Z scores may represent a useful clinical measure of SMM and are predictive of SO in this population. Our results are supportive of a functional muscle-bone unit in long-term survivors of pediatric ALL.