Role of the cardio-pulmonary exercise test and six-minute walking test in the evaluation of exercise performance in patients with late-onset Pompe disease

In patients with late-onset Pompe disease, we explored the role of the Cardiopulmonary Exercise Test (CPET) and of the Six-Minute Walking Test (6MWT) in the assessment of exercise capacity and in the evaluation of effects of enzyme replacement therapy (ERT). Eight patients affected by Late-onset Pompe disease, followed at a Centre for Neuromuscular Diseases and treated with ERT, underwent a baseline evaluation with a spirometry, a CPET and a 6MWT. Four of them were restudied after 36 months of treatment. All but one patients showed a reduction in exercise capacity as evaluated by peak oxygen uptake (VO2) measured at the CPET and Distance Walked (DW) measured at the 6MWT (median % predicted: 67.1 [range 54.3-99.6] and 67.3 [56.6-82.6], respectively). Cardiac and respiratory limitations revealed by the CPET were correlated to peak VO2, but not to the DW. Nevertheless, percent of predicted values of peak VO2 and DW were strongly correlated (rho=0.85, p=0.006), and close to identity. In the longitudinal evaluation forced vital capacity decreased, while peak VO2 and DW showed a trend to a parallel improvement. We concluded that although only the CPET revealed causes of exercise limitation, which partially differed among patients, CPET and 6MWT showed a similar overall degree of exercise impairment. That held true in the longitudinal assessment during ERT, where both tests demonstrated similar small improvements, occurring despite deterioration in FVC.