Which medical condition involves the formation and inflammation of muscle tissue?

The condition that involves the formation and inflammation of muscle tissue is myositis. Myositis is characterized by inflammation of the muscles, which can lead to swelling, pain, and muscle weakness. It can result from various causes, including autoimmune diseases, infections, or trauma.

While polymyositis does involve inflammation of multiple muscle groups, it is a specific subtype of myositis that affects the skeletal muscles more broadly. Choosing polymyositis indicates a narrower focus than the general term myositis, which applies to inflammation of muscle tissue regardless of the number of muscle groups involved.

In contrast, osteitis refers to inflammation of bone, and osteomalacia refers to the softening of bones due to vitamin D deficiency, neither of which pertain to muscle tissue. Therefore, myositis is the most accurate term for the condition described in the question.