Fig. 1: Clinical presentation, muscle imaging and histopathology.

A Schematic of affected front/back musculature in the proband suggestive of an FSHD pattern (areas highlighted in orange). Muscle MRI scan at age of 33 years. Right/left orientation is reported in coronal (B) and axial (C–G) scans (E). T1-weighted (B–F) and STIR (G) images. Acquisitions in the upper body showed trapezius (B, arrowhead) and pectoralis wasting (C, arrowhead) with sparing of spinati (B, dashed line) and subscapularis (C, dashed line) muscles. Biceps brachii (C, arrowhead) and latissimus dorsi (C, arrow) were also asymmetrically involved (arrowheads indicate severely involved muscles on the right and dashed lines less-affected muscles on the left). In the lower body, selective involvement of obliqui abdominis (D) was present on both sides, while iliopsoas was largely preserved, with only minor changes on the right (D, dashed line). The right thigh was significantly hypotrophic compared to the left one and displayed severe fatty replacement of adductors and posterior compartment muscles (E, arrowhead). Finally, the asymmetric involvement of the right tibialis anterior (F, arrowhead), which also presented hyperintense signal on STIR sequences (G, arrowhead), was the main abnormality in the lower leg. H Representative haematoxylin and eosin (H&E) staining highlighting the presence of necrotic fibres invaded by macrophages (arrowhead), scattered angulated fibres (small arrowheads), and overall increase in fibre size variability in the biopsy from right thigh muscle compared to the left.