Figure 1 Light microscopy findings   HE staining   The transverse section of the biceps brachii showed several ill- defined muscle fiber bundles, broad interstitial and severe muscle fiber atrophy (arrow indicates, Panel 1a).   × 100   There was a significant increase of myonuclides with internal displacement (arrow indicates, Panel 1b).   × 200

Figure 2 MRI findings of lower limb   Bilateral lower legs T₁WI showed reduced anterior muscle volume, moderate to severe fatty infiltration in tibialis anterior muscles, extensor digitorum longus, soleus muscles, and gastrocnemius (arrow indicates, Panel 2a). Bilateral lower legs T₂-STIR showed the above signals of muscle tissue decreased, indicating the fat component (Panel 2b). Bilateral thigh T₁WI showed reduced anterior muscle volume, moderate to severe fatty infiltration in vastus medialis, adductor magnus, sartorius, biceps femoris, and severe fatty infiltration in the quadriceps femoris (arrows indicate, Panel 2c). Bilateral thigh T₂-STIR showed the above signals of muscle tissue decreased, indicating the fat component (Panel 2d).

Figure 3 EMG showed myotonic potential, delayed action potential release occurred after activation of muscle fibers, and the frequency fluctuated from 20-100 Hz. It had fluctuations in frequency and amplitude.

Figure 4 TP-PCR fragment analysis of DMPK gene showed visible three-base gradient fragment peaks (> 100 CTG repeats).