Use of imaging to assess patients with muscle disease

PURPOSE OF REVIEW: A variety of imaging modalities can be used in muscle diseases. These range from plain x-rays to conventional magnetic resonance imaging (MRI) and phosphate magnetic resonance spectroscopy (MRS). This review places these imaging methods into their relevant clinical contexts on the basis of the best available research evidence. RECENT FINDINGS: Plain x-rays have limited roles in imaging patients with muscle disease. An exception is identifying calcinosis in patients with myositis; there is some evidence that effective early treatment may reduce its frequency and severity. Scintigraphy has been used in several centers but it appears to have limited value. Ultrasound, though successfully used in a number of units, is relatively little used, though the evidence suggests it would be sensible if this method were adopted more widely. MRI is currently the key imaging modality. It is useful in diagnosing pyomyositis, diabetic muscle infarction, and inflammatory myositis. Its main proven value is identifying the best sites for biopsy in early myositis, though it can help differentiate between different forms of muscle disease when there is diagnostic uncertainty. The area of most intense ongoing original research is MRS, which can show the bioenergetics of normal and abnormal muscles. Changes in the ratios of inorganic phosphate and phosphocreatine, particularly during exercise provide insights into the metabolic consequences of muscle diseases and may, in the future, suggest alternative therapeutic approaches. SUMMARY: Magnetic resonance imaging is a useful adjunct when diagnosing muscle diseases. It is particularly useful to identify suitable sites for muscle biopsy. Ultrasound may be equally helpful, though there is less supporting evidence from existing research. MRS is the area in which most current novel research is focused.