McArdle disease (glycogen storage disease type V) is a pure myopathy caused by an inherited deficit of myophosphorylase. The disease exhibits clinical heterogeneity, but patients typically experience exercise intolerance, acute crises of early fatigue, and contractures, sometimes with rhabdomyolysis and myoglobinuria, triggered by static muscle contractions or dynamic exercise. We present the case of a 54-year-old man with a lifelong history of fatigability, worsening on exertion. Laboratory evaluation revealed significant elevations in levels of creatine kinase (7924 U/L), lactate dehydrogenase (624 U/L), and myoglobulin (671 ng/mL). A muscle biopsy confirmed the presence of McArdle disease. This case report illustrates how, due to embarrassment, the patient hid his symptoms for many years and was eventually extremely relieved and “liberated” once McArdle disease was diagnosed 40 years later.
Glycogenosis type V, also known as glycogen storage disease type V (GSD V), myophosphorylase deficiency, or McArdle disease (Online Mendelian Inheritance in Man® [OMIM®; Johns Hopkins University, Baltimore, MD] number 232600), is a rare, mostly autosomal recessive disorder causing deficient myophosphorylation of glycogen in the skeletal muscles.1 Patients with McArdle disease have mutations in both alleles of the PYGM gene, which encodes myophosphorylase, the skeletal muscle isoform of glycogen phosphorylase.2 As the liver and heart isoforms of glycogen phosphorylase are unaffected, McArdle disease presents as a pure myopathy.3 Here, we report the case of a 54-year-old man with McArdle disease who had a long history of fatigability and exercise intolerance; he became unhappy and depressed because of not having an explanation for his symptoms for most of his life. We also summarize the main features of McArdle disease, including diagnostic tools and current therapeutic options.