Myopathies and cardiomyopathies: histochemical and biochemical analyses

The most frequent muscle diseases affecting the heart are muscular dystrophies and myotonic dystrophy. Apart from congenital heart diseases, various metabolic disorders are characterized by cardiac involvement. Potent candidates are carnitine deficiency, beta-oxidation deficiencies, and mitochondrial myopathies such as Kearns-Sayre syndrome. A typical example of an anaerobic metabolic myopathy causing cardiomyopathy is acid maltase deficiency. For diagnosis, ECG and echocardiography as well as cardiac catheterization should be performed and, if indicated, a heart muscle biopsy should be carried out. Diagnosis of the underlying disease should be possible from skeletal muscle biopsy. Besides routine staining, histology should include specific stainings for glycogen, lipids and mitochondrial activity or dystrophin. If certain histochemical abnormalities are found indicating a metabolic disorder, biochemistry is helpful for final diagnosis.