Using High‐Field Magnetic Resonance Spectroscopy to Measure Muscle Glycogen in Patients With McArdle Disease

INTRODUCTION/AIMS: Patients with McArdle disease demonstrate exercise intolerance with muscle contractures and episodic rhabdomyolysis. Additionally, some patients show progressive fat replacement of paraspinal and shoulder muscles with aging. The cause of fat replacement in older McArdle patients is unknown but could relate to a higher glycogen accumulation in these muscles in line with what is found in Pompe disease. The aim of the study was to investigate if this is also the case in McArdle disease, which could imply that excess levels of glycogen accumulation are a potential driver of fat replacement of muscle. METHODS: C magnetic resonance spectroscopy, we measured glycogen noninvasively in lumbar, thigh, and calf muscles in 14 patients with McArdle disease and 19 healthy controls. RESULTS: Patients with McArdle disease showed increased levels of glycogen in all muscles compared to controls; calf (3.2 times normal, p < 0.005), hamstrings (2.7 times normal, p < 0.005), anterior thigh compartment (2.7 times normal, p < 0.005), and lumbar muscle (2.1 times normal, p < 0.005). Glycogen was evenly distributed among muscle groups in both patients with McArdle disease and healthy controls. DISCUSSION: Our results are in line with previous studies showing two to three times increased glycogen compared to control in muscle biopsies. We found no variability in glycogen concentration among muscles that could indicate glycogen as a predictor of muscle injury in McArdle disease.