Morphologic aspects of fibromyalgia.

The most common morphological finding in muscle biopsies in longstanding fibromyalgia is type II fiber atrophy. This can be found in many other conditions such as disuse atrophy, affections of the corticospinal tracts, steroid atrophy, and other different neuromuscular disorders. An increase in lipid droplets and a slight proliferation of mitochondria in type I muscle fibers are correlated with the duration of fibromyalgia. In some cases we could find some ragged red fibers (RRF) which histochemically show a pronounced accumulation of lipids and mitochondria and single fiber defects of cytochrome-c-oxidase. In some fibromyalgia patients with RRF, we could find deletions of the mitochondrial genoma.