Marlene Busko

October 23, 2015

SEATTLE — In a large cohort of healthy, 65-year-old retirees, those with sarcopenia defined using some, but not other, proposed thresholds of lean-muscle mass had a heightened risk of short-term osteoporotic fracture.

Specifically, people who fell below the lean-muscle-mass cutoff proposed by Dr Richard N Baumgartner et al (Am J Epidemiol.1998;147:755-763) and by the European Working Group on Sarcopenia in Older People (EWGSOP 1) (Age Ageing.2010;39:412-423) had a significant 2.3-fold greater risk of having a low-trauma fracture within 3 years, Andrea Trombetti, MD, from the Geneva University Hospitals and Faculty of Medicine, Switzerland, reported in an oral session at the recent American Society for Bone and Mineral Research (ASBMR) 2015 Annual Meeting.

On the other hand, this new study — based on data from the Geneva Retirees Cohort (GERICO) — also showed that people classed as having sarcopenia defined using muscle-mass cutoffs put forth by EWGSOP 2, the International Working Group on Sarcopenia (IWG) (J Am Med Dir Assoc.2011;12:249-256), or the Foundation for the National Institutes of Health Sarcopenia Project (FNIH) (J Gerontol A Biol Sci Med Sci. 2014;69:547-558) did not have this enhanced risk of osteoporotic fractures.

"Our study demonstrated that besides classical risk factors, particularly bone-mineral density and FRAX score, the measurement of lean-[muscle] mass [and the thresholds defined by Baumgartner or EWGSOP 1] were able to predict…the occurrence of fractures," Dr Trombetti told Medscape Medical News.

However, "some of the cut points that were proposed in the literature were strongly associated with fracture, and others were not, so the threshold used is important," he stressed.

The divergent findings with different sarcopenia definitions does not mean that sarcopenia is not related to fracture risk, session comoderator and coauthor René Rizzoli, MD, from the Geneva University Hospitals and Faculty of Medicine, said.

"It means we should still work to have a consensus about the [lean-muscle-mass] threshold that would be applicable, not only worldwide but also from one race to another, because probably the threshold might be very different in very tall [whites] vs very small Asians," Dr Rizzoli told Medscape Medical News.

Differences in Defining Low Muscle Mass

Sarcopenia (age-related loss of muscle mass) is associated with an increased risk of falls, but there is ongoing debate about which definition of sarcopenia should be used, and it is unclear whether sarcopenia predicts fracture risk, said Dr Trombetti.

For example, Dr Baumgartner published the first definition of sarcopenia in 1998, based on a threshold of skeletal mass divided by height squared. Other definitions followed in 2010 (EWGSOP 1 and EWGSOP 2), 2011 (IWG), and 2014 (FNIH).

Dr Trombetti and colleagues aimed to investigate the prevalence of low lean-muscle mass and its association with 3-year fracture risk in the GERICO cohort, using these different proposed lean-muscle-mass thresholds to define sarcopenia.

They analyzed data from 913 healthy individuals (80% women) who lived in the community in Geneva, had a mean age of 65 years, and were enrolled in GERICO. Few (13%) had a body mass index (BMI) of 30 or more (obese), and their mean calcium intake was in the recommended range.

The participants had total and appendicular lean-muscle mass assessed by dual energy X-ray absorptiometry (DEXA), and the researchers computed FRAX from femoral bone-mineral density findings.

A total of 11% of study participants had lower-than-normal lean-muscle mass based on the Baumgartner or the EWGSOP 1 cutoffs (which are the same), Dr Trombetti reported.

However, 17% of participants had lower-than-normal lean-muscle mass based on the thresholds used by the EWGSOP 2 or the IWG. Only 3.5% of participants were below the lean-muscle mass cut point to define sarcopenia proposed by the FNIH.

Individuals with sarcopenia were less likely to be obese (especially women), and they tended to have a lower intake of protein or calcium. Women with sarcopenia had lower levels of parathyroid hormone.

Low Muscle Mass Associated With Increased Risk of Fracture

During an average follow-up of 3.4 years, 40 participants (4.4%) had at least one low-trauma fracture, defined as a fragility or osteoporotic fracture from a fall from a standing height or less, as opposed to a fracture after major trauma. The low-trauma fractures included a broken hip, collarbone, leg, arm, or wrist, for example, and excluded fractures of fingers and toes.

Compared with participants who did not have an incident low-trauma fracture, those who did had lower baseline total lean-muscle mass (41.2 vs 43.7 kg, P = .04) and lower baseline appendicular lean-muscle mass (17.2 vs 18.6 kg, P = .02).

Low muscle mass was associated with a significant increased risk of low-trauma fracture during follow-up, using Baumgartner or EWGSOP 1 thresholds for lean-muscle mass and adjusting for sex, age, length of follow-up, and FRAX (hazard ratio [HR], 2.3; 95% CI, 1.0–5.1, P = .05).

But after adjustment for the same confounders, low muscle mass was not associated with a significantly increased risk of low-trauma fracture using the EWGSOP 2 or IWG threshold (HR, 1.3; 95% CI, 0.6– 2.7; P > .05).

None of the patients with low lean-muscle mass based on FNIH criteria had a low-trauma fracture.

Dr Trombetti acknowledged that the researchers did not assess the subjects' physical performance at baseline; there were relatively few fractures, especially osteoporotic fractures; and the population had few comorbidities, so the findings may not be generalizable.

However, the study provides insight into a fairly homogeneous population of 65-year-olds, he said.

Future Directions

Further research is needed to see whether determining a person's muscle function would help predict their risk of low-trauma fracture, according to Dr Trombetti.

"In the geriatric field, [clinicians] are starting to measure gait speed and muscle [grip] strength, but this takes time, and most of the time it's not necessarily reimbursed by insurance," Dr Rizzoli noted.

Moreover, "what has to be demonstrated in this investigation done at the doctor's office" needs to predict "something that is clinically important for the patient…[such as] falls, death, rate of hospitalization, or rate of admission to nursing homes."

In future, "maybe it would be useful, at the same time [that clinicians] use densitometry [to measure bone density, they] should also measure the lean-[muscle] mass…to diagnose sarcopenia," Dr Trombetti speculated.

Drs Trombetti and Rizzoli have no relevant financial relationships.

American Society for Bone and Mineral Research 2015 Annual Meeting; Seattle, Washington. Abstract 1115, presented October 11, 2015.

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