[header] How to diagnose polymyositis [title] Take note of muscle weakness that worsens over several weeks. [step] Sore muscles are a part of everyone's life. However, muscle weakness that gradually worsens over a few weeks to a month may be a sign of pm. 
The possibility of pm further increases if the muscle weakness is widespread and on both sides of your body. [substeps] Pm most commonly occurs in the muscles of your shoulders, upper arms, hips, thighs, and neck.