Which histologic change is characteristic of chronic masticatory muscle myositis?

Which histologic change is characteristic of chronic masticatory muscle myositis?

• A. Fat infiltration
• B. Fibrosis of muscle tissue
• C. Acute inflammatory infiltrate
• D. Necrosis

Answer: (B)

In chronic masticatory muscle myositis the damage from the autoimmune attack accumulates over time and the muscle tissue that’s damaged is replaced by fibrous connective tissue. That fibrotic replacement is the hallmark of chronic disease, so histology shows muscle fibers that have been lost and replaced with collagen-rich stroma. In the early or active stage you might see inflammatory cells, but the defining feature of the chronic stage is fibrosis. Fat infiltration and necrosis can occur in other contexts or during different stages, but they do not represent the characteristic chronic change in this condition.

In chronic masticatory muscle myositis the damage from the autoimmune attack accumulates over time and the muscle tissue that’s damaged is replaced by fibrous connective tissue. That fibrotic replacement is the hallmark of chronic disease, so histology shows muscle fibers that have been lost and replaced with collagen-rich stroma. In the early or active stage you might see inflammatory cells, but the defining feature of the chronic stage is fibrosis. Fat infiltration and necrosis can occur in other contexts or during different stages, but they do not represent the characteristic chronic change in this condition.