Aerobic capacity in adult dermatomyositis/polymyositis patients and healthy controls

Abstract

Objective: Assessment of myositis patients has relied on symptoms, strength testing, and serum muscle enzyme activity. Recently, functional assessments and evaluation of strength by dynamometry and of disease activity by magnetic resonance imaging have also been added. Aerobic testing in selected patients has been considered useful.

Design: Case-control study.

Setting: University Hospital, Vienna, Austria.

Patients: Twenty-two subjects (8 outpatients with chronic dermatomyositis and 3 outpatients with chronic polymyositis, and 11 healthy controls) participated, allowing the identification of 11 case-control pairs matched by age (+/-3 years) and gender (mean age, 48+/-14 yrs; ratio of women to men, 18/4).

Main outcome measures: Target parameters were peak oxygen uptake (peak VO2) to estimate aerobic exercise capacity and peak isometric torque for muscle strength. Creatine phosphokinase (CPK) was measured to assess elevation of muscle enzymes.

Results: The mean peak VO2 in patients with dermatomyositis/polymyositis was 15.3 mL/min/kg (SD = 5.8) and in the healthy controls 28.7 mL/min/kg (SD = 7.8). Cardiorespiratory capacity expressed as peak VO2 was thus significantly reduced at 53% (p = .0001) of the control value. Muscle strength expressed as peak isometric torque was significantly lower (p = .01) in patients (mean 148+/-73 Nm) when compared to the control group (mean 261+/-99 Nm). In myositis patients peak VO2 and peak isometric torque correlate well with each other (r = .7631; p = .0001), but not at all with serum CPK levels (r = .056; p = .869).

Conclusion: Peak VO2 is significantly diminished in patients with dermatomyositis/polymyositis, compared with age- and sex-matched controls. Serum CPK did not significantly correlate with VO2. Aerobic exercise testing may be a useful assessment parameter in selected patients with dermatomyositis/ polymyositis.