What confirms the diagnosis of polymyositis?

The confirmation of a polymyositis diagnosis is primarily achieved through the detection of inflamed muscle fibers. This inflammation is a hallmark of the disease and is typically identified through muscle biopsy, which shows necrosis and inflammation in the muscle tissue. In polymyositis, the body's immune system mistakenly attacks muscle fibers, leading to weakness, pain, and inflammation.

Fluid in joints, high blood calcium levels, and normal muscle strength do not directly relate to the diagnosis of polymyositis. Joint fluid presence can be associated with other conditions, high calcium levels may indicate different metabolic issues, and normal muscle strength contradicts the very nature of polymyositis, in which muscle weakness is a key symptom. Therefore, the presence of inflamed muscle fibers in a biopsy is essential to confirming the diagnosis of polymyositis.