Background Exercise is increasingly utilized as a non-pharmacological intervention in the clinical management of patients with chronic inflammatory conditions. Availability of more objective microscopic outcome measures that provide functional information at the cellular, or even molecular, level would significantly strengthen ongoing efforts to tailor exercise interventions to individual patient needs and limitations. Significant proximal muscle weakness and exercise intolerance are prominent clinical features of Juvenile Dermatomyositis, with exercise intolerance and incomplete recovery persisting even in disease remission.(1) The use of a novel human whole-body exercise platform with concomitant dynamic 31P Magnetic Resonance Spectroscopy (MRS) assessments of quadriceps energy metabolism (2) may therefore provide additional insight into the underlying microscopic causes of exercise intolerance in this population.
Objectives (i) To evaluate whether MR spectroscopic evaluation of leg muscle energy and acid balance in vivo during dynamic bicycling exercise is feasible in a clinical setting and (ii) to determine the diagnostic merit of this technology in Juvenile Dermatomyositis.
Methods Eight children (mean age 15.9±1.5 SD years), 4 of whom were diagnosed with JDM in clinical remission (1F/3M) and 4 healthy age- and gender-matched peers, participated in the study. The female patient presented with idiopathic pain complaints following strenuous exercise. Two identical maximal supine bicycling tests were performed using an MR-compatible ergometer.(2) During the first test, cardiopulmonary performance was established in the exercise laboratory. During the second test, quadriceps energy balance and acid/base balance during incremental bipedal exercise and Phosphocreatine (PCr) recovery were determined using 31P MRS.
Results Quadriceps PCr and pH time courses during exercise and recovery were qualitative and quantitative similar in all but one patient experiencing idiopathic post-exercise pain. This patient demonstrated steeper and extensive PCr depletion and acidification during exercise. Strikingly, however, post-exercise PCr resynthesis was approximately twofold faster than control; indicating muscle tissue oxygenation abnormalities during exercise, rather than mitochondrial dysfunction.
Conclusions The results of the current study highlight the feasibility and potential of clinical whole-body exercise testing inside an MR scanner with concomitant 31P MRS assessments of quadriceps energy metabolism as a non-invasive screening platform for metabolic contraindications to exercise interventions in exercise intolerant patients with various inflammatory myopathies.
Takken T, van der Net J, Engelbert RH, Pater S, Helders PJ. Responsiveness of exercise parameters in children with inflammatory myositis. Arthritis Rheum 2008;59:59-64
JenesonJA, Schmitz JP, Hilbers PA, Nicolay K. An MR-compatible bicycle ergometer for in-magnet whole-body human exercise testing. Magn Reson Med. 2010;63:257-261.
Disclosure of Interest None Declared