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Abstract

Before genetic testing became widely available, the diagnostic workup of genetic muscle diseases traditionally included the histochemical analysis of muscle biopsies. With the advent of cheaper and more accessible genetic testing, the number of muscle biopsies for diagnostic purposes has declined. Interestingly, the application of another non-invasive diagnostic method, muscle imaging, especially muscle magnetic resonance imaging (MRI), is now also on the rise. The reasons for this are manifold. Standard axial T1 weighted and short tau inversion recovery (STIR) images are routine sequences on every scanner, quick to obtain and easy to interpret. In contrast to a muscle biopsy, lower limb or ideally whole body imaging allows for the assessment of muscle pathology across a large range of muscles. The non-invasive assessment is relatively cheap and can be performed longitudinally over the course of a disease. Over the past few years, more and more centres have applied muscle MRI to better understand the progression of muscle pathology over time, to identify selected patterns of muscle pathology that help to guide genetic testing and to use quantitative muscle MRI as an outcome measure in clinical trials to monitor the efficacy of therapeutic interventions. This presentation will focus on the diagnostic application of muscle MRI using primarily axial T1 weighted images of the lower limbs to illustrate how pattern recognition based on the selective involvement of muscles can help to guide genetic testing or support a specific diagnosis in case variants of uncertain clinical significance which have been identified in multiple genes. Muscle MRI scans can be especially helpful in the differential diagnosis of patients with congenital myopathies, myofibrillar myopathies, distal myopathies and limb girdle muscular dystrophies. They will often also allow to distinguish a primary muscle disease from a neuropathy or anterior horn cell disease and can in some cases almost be pathognomonic, as in collagen VI related Bethlem myopathy or in some RYR1-associated muscle diseases. The knowledge gained in some expert centres about the usefulness of muscle MRI as a diagnostic tool now needs to be widely disseminated for the benefit of neuromuscular clinicians, neurologist and radiologists. Ultimately, the imaging technique will hopefully help more patients to be accurately diagnosed.

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/content/papers/10.5339/qproc.2020.NMD.7
2020-09-15
2020-11-30
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