Figure 1.

Axial STIR (top) and T1W (below) images of the thigh muscles just above the knee showing bilateral asymmetrical muscle involvement. The right sartorius muscle (thin arrow) shows signal hyperintensity on the STIR images and some swelling consistent with oedema. Signal hyperintensity extends just beyond the anatomical margins of the muscles into the adjacent fascia. Signal changes on the T1W images are consistent with fatty infiltration. Similar changes are seen in the insertion of the left long head of biceps femoris (thick arrow). The remainder of the posterior compartment muscles are slightly small.