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Sporadic inclusion body myositis (s-IBM) is a chronic inflammatory myopathy of unknown pathogenesis. The common findings of ragged red fibres, cytochrome c oxidase-negative fibres and multiple mitochondrial DNA deletions in the muscle of patients with s-IBM have suggested that a deficit of energy metabolism may be of pathogenic relevance. To test this hypothesis we used 31P magnetic resonance spectroscopy to assess in vivo skeletal muscle mitochondrial function in the calf muscles of 12 patients with definite s-IBM. Eleven patients showed multiple mitochondrial DNA deletions in skeletal muscle and 67% showed ragged red fibres and/or cytochrome c oxidase-negative fibres. T1-weighted MR images showed increased signal intensity in the calf muscle of all patients except one. The involvement of calf muscle was confirmed by 31P magnetic resonance spectroscopy of resting muscle, which disclosed abnormalities in metabolite ratios in all patients. However, muscle oxidative metabolism assessed during recovery from exercise was normal in patients with s-IBM, as maximum rates of mitochondrial ATP production and post-exercise ADP recovery rates were within the normal range in all cases. We conclude that muscle mitochondrial abnormalities are a secondary process and unlikely to play a significant role in the pathogenesis of s-IBM.

Type

Journal article

Journal

Brain

Publication Date

11/1998

Volume

121 ( Pt 11)

Pages

2119 - 2126

Keywords

Adenosine Diphosphate, Adenosine Triphosphate, Adult, Age of Onset, Aged, DNA, Mitochondrial, Energy Metabolism, Female, Humans, Magnetic Resonance Imaging, Magnetic Resonance Spectroscopy, Male, Middle Aged, Mitochondria, Muscle, Muscle, Skeletal, Myositis, Inclusion Body, Oxygen Consumption, Phosphates, Phosphocreatine, Phosphorus, Physical Exertion, Reference Values, Sequence Deletion