3 - Mitochondrial myopathies: clinical features, investigation, treatment and genetic counselling

Abstract

Publisher Summary This chapter discusses the clinical features, investigation, treatment, and genetic counselling of mitochondrial myopathies. The mitochondrial myopathies are a clinically diverse group of diseases defined historically by the presence of structural mitochondrial abnormalities in biopsied skeletal muscle. The histological hallmark of mitochondrial myopathy is the ragged red fiber (RRF), demonstrated with the modified Gomori trichrome stain, containing peripheral and intermyofibrillar accumulations of abnormal mitochondria. Although the diagnostic importance of muscle biopsy is undisputed, the presence of RRFs as a sole criterion for establishing the diagnosis has been challenged by recent histochemical, biochemical, and genetic advances. RRFs occur in patients with clinical syndromes predominantly or exclusively involving the central nervous system (CNS). Patients may present with psychomotor retardation, dementia, seizures, ataxia, movement disorders, and stroke like episodes, pigmentary retinopathy, deafness, and peripheral neuropathy in various combination. Subsets of clinical features within the spectrum of mitochondrial encephalomyopathies lead to the identification of apparently specific clinicopathological entities. Involvement of tissues other than muscle, nerve, and CNS has further broadened the spectrum of mitochondrial myopathies to include hematological, endocrine, renal, cardiac, gastrointestinal, and metabolic manifestations.