Mid-Arm Muscle Size Predicts Survival in MHD Patients
Higher mid-arm muscle circumference (MAMC) is a surrogate of larger lean body mass that independently predicts greater survival and mental health in patients on maintenance hemodialysis (MHD), according to investigators.
In a study of 792 MHD patients with a mean age of 56 years, researchers led by Kamyar Kalantar-Zadeh, MD, PhD, MPH, of the University of California in Los Angeles, looked at the associations of triceps skin fold (TSF), MAMC, and serum creatinine (another lean body mass surrogate) with five-year survival and quality of life (QOL). Lean body mass was measured using dual-energy x-ray absorptiometry in a subset of 118 randomly selected patients. The researchers used the Short Form 36 (SF36) to assess QOL.
Compared with patients in the first quartile of MAMC, subjects in the second, third, and fourth quartiles had a 14%, 31%, and 37% decreased risk of five-year mortality, respectively, a trend that was significant even after adjusting for case-mix, malnutrition-inflammation-cachexia syndrome, and inflammatory markers, Kalantar-Zadeh's team reported online in the Clinical Journal of the American Society of Nephrology. Higher MAMC was significantly associated with better scores on the SF36 mental health scale.
Using median values of MAMC and TSF, the investigators looked at the effect of various combinations of low and high MAMC and TSF on five-year mortality. Compared with patients who had low MAMC and low TSF, those with high MAMC and low TSF had a significant 41% decreased risk of five-year mortality. Patients with high MAMC and high TSF had a significant 48% decreased risk.
In addition, higher serum creatinine levels and larger TSF were associated with reduced five-year mortality, but these associations were mitigated after adjusting for multiple variables.
As to why muscle mass may be associated with better survival, the authors cited evidence showing that low muscle mass may reflect poor nutritional status. It also may reflect higher levels of or unopposed inflammation because muscle may confer anti-inflammatory effects in MHD patients, although Dr. Kalantar-Zadeh's group noted that their study found no correlation between low muscle mass and lower concentrations of inflammatory markers. Additionally, higher muscle mass is associated with higher non-edema-related body water, which can dilute circulating toxins and cytokines. Consequently, patients with lower muscle mass may have a higher concentration of uremic toxins.
Another possible explanation is that increased muscle mass is associated with physical activity and exercise training. Exercise can improve arterial stiffness in MHD patients, the authors explained, and arterial stiffness is an independent predictor of cardiovascular disease and death in MHD patients.