The clinical course of metabolic myopathies is dominated by progressive muscle weakness and wasting or aching contraction and recurrent rhabdomyolysis with intense exercise. Vacuolar muscle fibre degeneration is the leading pathological finding on routine histological examination. For further characterization of those histologically empty looking vacuoles, histochemistry and electron microscopy are employed. Increase of glycogen, lipid droplets or mitochondria can often be demonstrated and indicate the need for subsequent biochemical identification of the underlying metabolic defect. Some other metabolic myopathies that cause recurrent rhabdomyolysis lack myopathological abnormalities. These can only be diagnosed biochemically, but additional new histochemical screening methods might be helpful.
Biopsy Contracture