Glycogenolytic myopathy

Metabolic myopathies due to abnormalities of energy metabolism may be due glycogenolytic or mitochondrial abnormalities.

• glycogenolytic: microphosphorylase and phosphofructose deficiency are examples of glycogenolytic causes of myopathy. Muscle pain occurs during high intensity or ischaemic contractions. There may be contracture and rhabdomyolysis if ischaemia continues. Patients may complain of difficulty starting exercise or exercising at high intensity, but exercise normally at low workloads.
  
  
• mitochondrial: patients may complain of wide range of symptoms including low exercise tolerance, muscle pain, weakness, and external ophthalmoplegia. Muscle biopsies of these patients show 'ragged red fibre' and the precise biochemical lesion may be determined on isolates of mitochondria.