ragged red fibres
A term referring to an abnormality seen by light microscopy in frozen sections of skeletal muscle in mitochondrial encephalomyopathies stained with Gomori trichrome. The red colour is due a compensatory proliferation of abnormal mitochondria. The abnormal fibres are coarse and vacuolated and disorganised (“ragged”) at the periphery.
Electron microscopy shows clusters of large, irregular mitochondria with degenerated cristae and unique crystalloid inclusions.
The histopathological changes are accompanied by various defects in the mitochondrial electron transport chain, including mitochondrial ATPase, NADH-coenzyme Q reductase, cytochrome oxidase b and cytochrome oxidase c with crystal-like inclusions.
Images by Dimitri Agamanolis, MD