Imaging Tools for the Assessment of Idiopathic Inflammatory Myositis
Imaging Tools for the Assessment of Idiopathic Inflammatory Myositis
Purpose of Review: To summarize advances in the imaging of idiopathic inflammatory myopathies.
Recent Findings: T2-weighted MRI with fat suppression or short tau inversion recovery sequences are the most sensitive and specific routine method of polymyositis and dermatomyositis imaging. MRI also represents an important aid in the identification of biopsy sites, with whole-body MRI sensitively visualizing the distribution of muscle involvement throughout the body. Ultrasound may be a cost-effective alternative to MRI, with contrast-enhanced ultrasound also permitting the assessment of muscle vascularization. PET sensitively detects increased muscle metabolism and simultaneously screens for underlying malignancies in dermatomyositis. Most scintigraphic techniques have a low sensitivity and specificity in the detection of muscle involvement, and it is unclear whether they provide an added benefit. New MRI techniques, such as T2 mapping, diffusion-weighted imaging and blood oxygenation level-dependent imaging, can provide information on muscle recruitment, myofibrillar structure and blood supply.
Summary: In suspected myositis, muscle imaging should be strongly considered prior to obtaining a muscle biopsy. Future research should prospectively study the use of muscle imaging in the evaluation of treatment response and muscle function.
The term 'idiopathic inflammatory myopathy' in its narrow sense denotes polymyositis, dermatomyositis and inclusion body myositis (IBM); in its broader sense, the term also includes a number of other inflammatory muscle disorders. In the work-up of many myopathies, it is important to diagnose or rule out dermatomyositis and polymyositis because these disorders are in contrast to many other myopathies amenable to treatment.
The diagnosis of inflammatory myopathies usually hinges on the presence of several criteria and mostly requires a muscle biopsy. Because the distribution of muscle inflammation within a muscle group may be heterogeneous and, in the idiopathic inflammatory myopathies, may even be confined to a single muscle, muscle imaging is particularly useful in identifying a promising biopsy site and thus reduces the sampling error of untargeted biopsies.
The following sections will provide an update of the advances in different muscle imaging techniques whose costs have increased disproportionally as compared with overall medical costs. The focus of the present review is on the diagnostic utility of muscle imaging and new developments for functional assessment.
Purpose of Review: To summarize advances in the imaging of idiopathic inflammatory myopathies.
Recent Findings: T2-weighted MRI with fat suppression or short tau inversion recovery sequences are the most sensitive and specific routine method of polymyositis and dermatomyositis imaging. MRI also represents an important aid in the identification of biopsy sites, with whole-body MRI sensitively visualizing the distribution of muscle involvement throughout the body. Ultrasound may be a cost-effective alternative to MRI, with contrast-enhanced ultrasound also permitting the assessment of muscle vascularization. PET sensitively detects increased muscle metabolism and simultaneously screens for underlying malignancies in dermatomyositis. Most scintigraphic techniques have a low sensitivity and specificity in the detection of muscle involvement, and it is unclear whether they provide an added benefit. New MRI techniques, such as T2 mapping, diffusion-weighted imaging and blood oxygenation level-dependent imaging, can provide information on muscle recruitment, myofibrillar structure and blood supply.
Summary: In suspected myositis, muscle imaging should be strongly considered prior to obtaining a muscle biopsy. Future research should prospectively study the use of muscle imaging in the evaluation of treatment response and muscle function.
The term 'idiopathic inflammatory myopathy' in its narrow sense denotes polymyositis, dermatomyositis and inclusion body myositis (IBM); in its broader sense, the term also includes a number of other inflammatory muscle disorders. In the work-up of many myopathies, it is important to diagnose or rule out dermatomyositis and polymyositis because these disorders are in contrast to many other myopathies amenable to treatment.
The diagnosis of inflammatory myopathies usually hinges on the presence of several criteria and mostly requires a muscle biopsy. Because the distribution of muscle inflammation within a muscle group may be heterogeneous and, in the idiopathic inflammatory myopathies, may even be confined to a single muscle, muscle imaging is particularly useful in identifying a promising biopsy site and thus reduces the sampling error of untargeted biopsies.
The following sections will provide an update of the advances in different muscle imaging techniques whose costs have increased disproportionally as compared with overall medical costs. The focus of the present review is on the diagnostic utility of muscle imaging and new developments for functional assessment.
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