Skeletal Muscle, McArdle disease [LMP91588]

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Diagnostic Modality: 
Whole Slide Image
Disease Category: 
Genetic Disorders
Diagnosis: 
McArdle disease
Species: 
Human
Organ System: 
Peripheral Nerve and Skeletal Muscle
Gender: 
Male
Age: 
45 years
Diagnosis Code: 
ICD-10: E74.0
Slide Contributor Information
Gao, A., Keith, J.

Keywords

Glycogen storage disease type V, GSD-V, muscle glycogen phosphorylase, myophosphorylase deficiency

Clinical History

45-year-old man with recurrent rhabdomyolysis, exercise intolerance, and second wind phenomenon.

Clinical Discussion

McArdle disease is a glycogen storage disease (GSD type V) caused by inactivating mutations in the muscle-specific isoform of glycogen phosphorylase (myophosphorylase, PYGM, 11q13.1). This results in the inability to break down glycogen but McArdle disease is unique among GSDs in that it exclusively affects skeletal muscle. It is also one of the most common GSDs, although the prevalence is only 1 in 100,000. Patients typically present in childhood or adulthood with exercise intolerance, muscle pain, rhabdomyolysis, and a characteristic “second wind” phenomenon. Microscopically, muscle biopsy shows general myopathic features along with PAS-positive diastase-sensitive subsarcolemmal vacuoles that contain non-membrane bound glycogen on electron microscopy. Histochemistry for myophosphorylase shows absent enzyme activity but must be interpreted along with an appropriate positive control (checkerboard staining pattern). Treatment is generally supportive and with lifestyle changes.

See Related Content for PAS and PASD stains.

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PAS stain
PASD stain