Treatment and Management of Hereditary Metabolic Myopathies

Hereditary metabolic myopathies encompass a group of disorders that result from a shortage of energy production in muscle cells. Biochemical defects are located in glucose/glycogen or lipid metabolism or in the mitochondrial respiratory chain. Thus, metabolic myopathies can be subdivided into glycogenosis, disorders of lipid metabolism, and mitochondrial myopathies. Exercise-induced muscle weakness, myalgia, and rhabdomyolysis with myoglobinuria are characteristic symptoms. However, permanent weakness is also frequent. Multisystemic manifestations beyond muscle manifestation are possible, especially in mitochondrial disorders. Many different, sometimes very rare, enzyme defects are known to cause metabolic myopathies. Frequent disorders are myophosphorylase deficiency (McArdle disease), acid α-glucosidase deficiency (Pompe disease), carnitine palmitoyltransferase II deficiency, and chronic progressive external ophthalmoplegia. In addition to the detailed description of these disorders, this chapter also covers the management of rhabdomyolysis. Although next-generation sequencing techniques facilitated genetic testing, muscle biopsy, not only for histological but also for biochemical examination and genetic testing of mitochondrial DNA, is still helpful in diagnostic workup. Causal treatment is possible in Pompe disease: Enzyme replacement therapy can stabilize the disease. In certain metabolic myopathies, substitution of vitamins or coenzymes is effective. Sometimes, dietary measures reduce symptoms.