Relationship between muscle inflammation and fat replacement assessed by MRI in facioscapulohumeral muscular dystrophy
Unlike most muscular dystrophies that progress symmetrically at a constant rate, facioscapulohumeral muscular dystrophy (FSHD) is characterized by stepwise, asymmetric progression of muscle wasting, and weakness. Muscle tissue is progressively replaced by fat; however, its relation to preceding inflammation is unclear. In this longitudinal study of FSHD, we assessed muscle inflammation and fat replacement and their relation quantitatively. We also investigated whether fat replacement in muscle varies along its length.
Forty-five patients with FSHD were evaluated twice, 14 months apart. Using MRI sequences with short TI inversion recovery (STIR), we quantified the degree of STIR hyperintensity in muscles (≥ 2 SD above control intensity). STIR hyperintensities (STIR+) suggest edema or inflammation. We used Dixon MRI to quantify fat content.
Of 370 thigh muscles, 83 were STIR+ at baseline and 103 at follow-up. The highest frequency of STIR+ was seen in muscles with inter-mediate fat content (40–60% fat). The progression of fat replacement was higher in STIR+ muscles (5.0 ± 4.0%) vs. STIR− muscles [2.3 ± 3.3% (P < 0.0001)]. In addition, muscles with severe STIR+ at baseline had a higher fat replacement progression than muscles with milder STIR+ (R = 0.39, P = 0.001). The fat content was higher in the distal part vs. proximal part of most muscles (P < 0.05). However, the progression of the fat replacement was uniform along the length of all the muscles.
Muscles with STIR+, indicating inflammation, have a faster progression of fat replacement than STIR− muscles, and the fat replacement progression correlated with the severity of STIR+.
KeywordsFacioscapulohumeral muscular dystrophy FSHD MRI STIR Dixon
Analysis of variance
Facioscapulohumeral muscular dystrophy
Short TI inversion recovery
No STIR hyperintensity
The authors thank Poul Henrik Frandsen, radiologist, Department of Diagnostic Radiology, Rigshospitalet, for his helpful advice in setting up the MRI protocol. This study has been funded by the Augustinus foundation.
JRD: conception and design of the study, acquisition and analysis of data, drafting the text, and preparing the figures. GA: conception and design of the study, acquisition of data, and analysis of data. TK: acquisition and analysis of data. CV: acquisition and analysis of data. CT: design of the study and analysis of data. JV: conception and design of the study, design of manuscript, and reviewing.
Compliance with ethical standards
Conflicts of interest
The authors declare that they have no conflict of interest related to this study.