Longitudinal features of stir bright signal in FSHD¹

Introduction: Magnetic resonance imaging of muscle shows short tau-inversion recovery (STIR) brightness in autosomal dominant facioscapulohumeral muscular dystrophy (FSHD1) suggestive of active inflammation/injury. We measured the longitudinal stability/progression of this potential disease biomarker. Methods: Nine subjects underwent calf MRI imaging over 2 years. Two radiologists evaluated qualitative muscle changes. Results: In 3/9 subjects, calf muscles demonstrated moderate/severe STIR hyperintensity at Time 1 that had progressed to fatty replacement 2 years later (Time 2). In the remaining subjects, moderate/severe muscle STIR abnormalities, when present, were consistent between exams. Mild STIR+ elevations had roughly similar patterns between exams. Conclusions: Moderate/severe STIR hyperintensities often foreshadow fatty replacement over a 2-year interval. Whether longer time courses are required to observe muscle degeneration and fatty replacement in some subjects remains to be explored.