Myopathies represent a heterogeneous group of skeletal muscle disorders characterized by morphological and functional changes in the muscle, such as replacement of muscle tissue by connective tissue, fatty infiltration, and/or inflammation.
Current imaging modalities used in neuromuscular imaging include computed tomography, ultrasound, and magnetic resonance imaging (MRI). (Caetano el at, 2019)
MRI is becoming more frequently used in studies involving measurements of adipose tissue and volume and composition of skeletal muscles. (Borga, 2018)
The basic approach to muscle MRI interpretation includes evaluation of muscle shape, volume, and signal intensity on both T2-weighted STIR and T1-weighted images.
Expected general muscle volume and signal, adjusted according to age, are evaluated first, followed by the volume and signal of every single muscle and muscle group, compared to surrounding and contralateral structures.
For T2- weighted sequences, increased signal intensity is found when muscle edema is present, while increased signal intensity on T1-weighted images is observed in muscle undergoing fatty degeneration. (Cejas et al, 2017)
Cejas CP, Serra MM, Galvez DFG, Cavassa EA, Taratuto AL, Vazquez GA, Massaro MEL, Schteinschneider AV. Muscle MRI in pediatrics: clinical, pathological and genetic correlation. Pediatr Radiol. 2017 May;47(6):724-735. doi: 10.1007/s00247-016-3777-6. Epub 2017 Jan 19. PMID: 28102454.
Caetano AP, Alves P. Advanced MRI Patterns of Muscle Disease in Inherited and Acquired Myopathies: What the Radiologist Should Know. Semin Musculoskelet Radiol. 2019 Jun;23(3):e82-e106. doi: 10.1055/s-0039-1684022. Epub 2019 Jun 4. PMID: 31163512.
Borga M. MRI adipose tissue and muscle composition analysis-a review of automation techniques. Br J Radiol. 2018 Sep;91(1089):20180252. doi: 10.1259/bjr.20180252. Epub 2018 Jul 24. PMID: 30004791; PMCID: PMC6223175.