MRI findings in IIMs. All images are axial STIR images of the left thigh, and the small boxes in the lower left are magnified images of the corresponding MRI findings. (A) Fascial pattern: Linear HSI localises to the fasciae. Fascial patterns can be distinguished from chemical shift artefacts, generally localised to only one side of the fasciae. (B) Peripheral pattern: HSI areas are observed in the marginal zone of the muscles, and the signal intensity continuously decreases inward. (C) Honeycomb pattern: HSI areas are mainly observed in the rectus femoris and vastus lateralis with reticular HSI. (D) Foggy pattern: Relatively homogeneous HSI areas are observed in the muscle parenchyma. In this case, HSI areas occupy >50% of muscle parenchyma, and the distribution is diffuse. (E) Dense dot pattern: punctate HSI is densely clustered in the muscle parenchyma. A patchy honeycomb pattern is also observed in the adductor magnus (arrow). (F) Coarse dot pattern: Punctate HSI is sparsely scattered in the muscle parenchyma (arrowhead). The adjacent linear HSI (arrow) represents a small vessel and can be traced in continuous axial sections (image not shown). IIMs: idiopathic inflammatory myopathies; STIR: short TI inversion recovery