How does polymyositis affect the shoulder and pelvic muscles?

Polymyositis is a chronic, progressive muscle disease characterized by the inflammation and degeneration of skeletal muscle, specifically targeting the muscles of the shoulder and pelvic girdles.12

The pathology of the disease affects these muscles in the following ways:

• Initial Symptoms: Affected muscles may initially become slightly swollen, leading to muscle weakness and, in some cases, pain. This weakness typically manifests in the muscles closest to the torso.1
• Progression: As the condition advances, the affected shoulder and pelvic muscles undergo atrophy (wasting away) and hardening.1
• Functional Impact: The degeneration can eventually lead to the development of contractures, further impairing muscle function.2

The underlying damage is believed to be an autoimmune response where T lymphocytes attack the muscle tissue. Diagnosis is often supported by elevated levels of enzymes released into the bloodstream during the destruction of muscle fibers and confirmed through microscopic examination of the tissue.12