Aerobic capacity in adult dermatomyositis/polymyositis patients and healthy controls

Objective: Assessment of myositis patients has relied on symptoms, strength testing, and serum muscle enzyme activity. Recently, functional assessment s and evaluation of strength by dynamometry and of disease activity by magn etic resonance imaging have also been added. Aerobic testing in selected pa tients has been considered useful. Design: Case-control study. Setting: University Hospital, Vienna, Austria. Patients: Twenty-two subjects (8 outpatients with chronic dermatomyositis a nd 3 outpatients with chronic polymyositis, and 11 healthy controls) partic ipated, allowing the identification of 11 case-control pairs matched by age (+/-3 years) and gender (mean age, 48 +/- 14yrs; ratio of women to men, 18 /4). Main Outcome Measures: Target parameters were peak oxygen uptake (peak (V) over dot O-2) to estimate aerobic exercise capacity and peak isometric torq ue for muscle strength. Creatine phosphokinase (CPK) was measured to assess elevation of muscle enzymes. Results: The mean peak (V) over dot O-2 in patients with dermatomyositis/ p olymyositis was 15.3mL/min/kg(SD = 5.8) and in the healthy controls 28.7 mL /min/kg (SD = 7.8). Cardiorespiratory capacity expressed as peak (V) over d ot O-2 was thus significantly reduced at 53% (p =.0001) of the control valu e. Muscle strength expressed as peak isometric torque was significantly low er (p =.01) in patients (mean 148 +/- 73 Nm) when compared to the control g roup (mean 261 +/- 99Nm). In myositis patients peak (V) over dot O-2 and pe ak isometric torque correlate well with each other (r =.7631; p =.0001), bu t not at all with serum CPK levels (r =.056; p=.869). Conclusion: Peak (V) over dot O-2 is significantly diminished in patients w ith dermatomyositis/polymyositis, compared with age- and sex-matched contro ls. Serum CPK did not significantly correlate with (V) over dot O-2 Aerobic exercise testing may be a useful assessment parameter in selected patients with dermatomyositis/ polymyositis.