IMPAIRMENT OF THE EXERCISE-INDUCED INCREASE IN MUSCLE PERFUSION IN MCARDLES-DISEASE

In McArdle's disease (myophosphorylase deficiency) exercise intoleranc e is generally attributed to a lack of glycogenolysis, which decreases energy production during exercise. Magnetic resonance imaging data ha ve recently suggested an impairment of the increase in muscle perfusio n during exercise in these patients. We have tested this hypothesis by direct measurement of local muscle perfusion increase. Increase in mu scle perfusion was assessed by positron emission tomography with oxyge n-15 labelled water in five patients with McArdle's disease and five a ge- and sex-matched healthy volunteers. Radioactivity was measured in both forearms before and after exercise of the right forearm. The exer cise intensity was biochemically assessed by in vivo phosphorus-31 mag netic resonance spectroscopy. The estimated increase in muscle perfusi on with exercise was 5.7+/-5.5-fold in the patients (range 1.5-12.8) a nd 22.3+/-12.0-fold in the healthy subjects (range 10.1-37) (P=0.022). The results show a significant impairment of increase in muscle perfu sion with exercise in McArdle's disease. Thus patients may suffer not only from a direct lack of glycogenolysis but also from indirectly imp aired vasodilation.