Cardiorespiratory fitness in long-term juvenile dermatomyositis: a controlled, cross-sectional study of active/inactive disease.

Objectives: To compare cardiorespiratory fitness (CRF) expressed as maximal oxygen uptake (VO2max) between patients with long-term JDM and controls and between patients with active and inactive disease, as well as to explore exercise limiting factors and associations between CRF and disease variables.

Methods: JDM patients (n = 45) and age- and gender-matched controls (n = 45) performed a cardiopulmonary exercise test (CPET) on a treadmill until exhaustion. Physical activity was measured by accelerometers. Disease activity, damage and muscle strength/function were assessed by validated tools. Clinically inactive disease was defined according to PRINTO criteria.

Results: The mean disease duration was 20.8 (s.d. 11.9) years and 29/45 (64%) patients had inactive disease. A low VO2max was found in 27% of patients vs 4% of controls (P = 0.006). The mean VO2max and maximal ventilation (VEmax) were lower in patients with active and inactive disease compared with controls. Patients with active disease also had lower maximal voluntary ventilation (MVV) compared with controls and lower VEmax and MVV compared with those with inactive disease. Patients with inactive disease had lower physical activity levels compared with controls. VO2max correlated negatively with disease damage in patients with inactive disease and positively with muscle strength/function in patients with active disease.

Conclusion: CRF was lower in JDM patients, both with active and inactive disease, compared with controls after a mean 20 years disease duration. Cardiopulmonary exercise test results suggested different limiting factors contributing to the reduced CRF according to disease activity, including deconditioning in inactive disease and reduced ventilatory capacity in active disease. Further research is needed to verify this.