McArdle Disease: Safe Activity, Muscle Injury and RN Care

McArdle disease, also called glycogen storage disease type V (GSD V) or myophosphorylase deficiency, is an inherited metabolic myopathy caused by pathogenic variants in both copies of the PYGM gene. PYGM codes for muscle glycogen phosphorylase, the enzyme that releases glucose units from glycogen stored inside skeletal muscle. Without it, working muscle cannot use its own glycogen for fuel. The typical result is exercise intolerance: disproportionate pain, early fatigue, stiffness or a painful contracture in the first minutes of activity, even when strength at rest looks normal. The international clinical practice guideline (2021) reports an estimated prevalence of about 1 in 100,000 from genetic data in the Dallas-Fort Worth area and about 1 in 139,543 from diagnosed cases in Spain. Population sequencing data suggest a higher genetic frequency, between 1 in 7650 and 1 in 42,355, which points to underdiagnosis. Symptoms usually begin in the teens or twenties but can appear at any time from infancy to adulthood. Many people describe years of being called lazy or unfit before diagnosis. MedlinePlus Genetics reports that about half of people with GSD...