Mitochondrial myopathies-clinicopathological features and diagnostic modalities.

Mitochondrial myopathy is the term applied to a clinically and biochemically heterogeneous group of disorders which have multisystem involvement. The concept was introduced by Luft in 1962. These are due to genetic defects in the respiratory chain enzymes which are detected by histochemical, immunohistochemical stains, molecular biological studies and ultrastructural studies on muscle biopsy. Classification of the disorders can be genetic, based on defects of respiratory enzyme complexes or on the basis of the clinical syndromes. Due to the extremely variable clinical presentations of these disorders, a complete clinical and laboratory workup involving strict diagnostic criteria is essential.