P.17.17 McArdle disease with pronounced axial myopathy

Abstract

McArdle disease is the most common non-lysosomal glycogenosis and have classically onset in childhood with exercise-induced pain. Fixed weakness can manifests from around fifty years of age but is typically mild and located around the shoulder girdle. We describe a 61 year old man with exercise-induced pain from childhood who was referred to us due to 5 years progressive muscle wasting and elevated creatine kinase to 4000U/l. On investigation he was severely atrophic and weak in his shoulder girdle and the entire paraspinal musculature. MRI confirmed that the paraspinal musculature was all converted to fat. Muscle biopsy was myopathic with negative myophosphorylase stain and multiple large vacuoles with glycogen. A non-ischemic forearm exercise test showed a small decrease in lactate together with an exaggerated ammonium elevation. Genetic testing revealed two previously described mutations in the PYGM gene verifying the suspicion of McArdle disease. This very unusual presentation of McArdle disease demonstrates that these patients can have pronounced wasting of paraspinal musculature. We suspect that this is related to the unusual high amount of glycogen vacuoles and stress the importance of including McArdle disease in the differential diagnose of axial myopathy.