AssessmentsGlycogen storage disease type V
Glycogen storage disease type V
USMLE® Step 1 style questions USMLE
A 20-year-old man comes to the emergency department with painful muscle spasms. He notices that these episodes worsen after a run and seem to improve after brief periods of rest. His past medical history includes a right knee ACL tear. His temperature is 37.0°C (98.6°F), pulse is 80/min, respirations are 16/min, and blood pressure is 125/75 mmHg. Abdominal examination is unremarkable. Rapid fingerstick glucose is 80 mg/dL. Serum creatine kinase levels are elevated. Laboratory investigations are shown below:
|Creatine kinase||645 U/L|
|Fractional excretion of sodium (FENa)||>2%|
Electrocardiogram and echocardiogram are unremarkable. Which of the following is the most likely diagnosis?
Glycogen storage disease type V, also known as McArdle's disease, is a glycogen metabolism disorder in which an enzyme known as muscle phosphorylase (myophosphorylase) is deficient. Muscle phosphorylase is necessary to break down glycogen stored in muscles into usable glucose. People with Glycogen storage disease type V can present with rhabdomyolysis, myoglobinuria, exercise intolerance, and muscle weakness.