 Muscle biopsy can be useful if an episode of rhabdomyolysis is thought to be the result of an underlying muscle disorder . A biopsy sample taken during an episode is often uninformative , as it will show only evidence of cell death or may appear normal . Taking the sample is therefore delayed for several weeks or months . The <unk> appearance on the biopsy indicates the nature of the underlying disorder . For instance , mitochondrial diseases are characterized by ragged red fibers . Biopsy sites may be identified by medical imaging , such as magnetic resonance imaging , as the muscles may not be uniformly affected . 
