McArdle's disease: Diagnostic approach after clinical symptoms of vigorous exercise intolerance in a snowboarder in Alpes

McArdle's disease (glycogen storage disease type V) is an energy-dependent disorder of skeletal muscle caused by a deficiency of myophosphorylase, an important enzyme of carbohydrate metabolism that converts glycogen to glucose-1-phosphate. A 46 year-old man was sent to the rheumatology outpatient department with a 3-year history of severe exercise-induced cramps and myalgias. The episodes began when he worked in France and used to practice ski and snowboard in the Alps Mountain, with exercise intolerance, muscle cramps, and myoglobinuria. The laboratory results showed elevated serum creatine kinase levels (∼15,000 U/L), and the biopsy of the deltoid muscle revealed glycogen subsarcolemmal vacuoles and absence of myophosphorylase enzymatic activity. This clinical case emphasises the importance of taking into account this metabolic disorder when faced with a patient with exercise intolerance and cramps, especially after vigorous/anaerobic exercise and elevated levels of CK activity. It is fundamental to explain the aetiology of the patient symptoms in order to improve quality of life and avoid unnecessary complications.