What is the underlying pathophysiology generally associated with masticatory muscle myositis?

What is the underlying pathophysiology generally associated with masticatory muscle myositis?

• A. Autoimmune process targeting Type 1 muscle fibers
• B. Bacterial infection of the muscle
• C. Immune mediated process targeting type 2M muscle fibers
• D. Nutritional deficiency causing muscle atrophy

Answer: (C)

Masticatory muscle myositis is an autoimmune inflammatory disease where the immune system specifically targets a protein called the type 2M myosin heavy chain present in the jaw (masticatory) muscles. This targeted immune attack causes ongoing injury and loss of those muscle fibers, leading to swelling, pain, and progressive weakness of the jaw muscles that can limit opening the mouth. Because the pathology is a immune-mediated destruction of these exact fibers, it’s not caused by a bacterial infection, not a general deficiency of Type 1 muscle fibers, and not due to nutritional atrophy. The specificity to Type 2M fibers explains why the disease is confined to masticatory muscles and why tests often look for autoantibodies against the 2M myosin.

Masticatory muscle myositis is an autoimmune inflammatory disease where the immune system specifically targets a protein called the type 2M myosin heavy chain present in the jaw (masticatory) muscles. This targeted immune attack causes ongoing injury and loss of those muscle fibers, leading to swelling, pain, and progressive weakness of the jaw muscles that can limit opening the mouth. Because the pathology is a immune-mediated destruction of these exact fibers, it’s not caused by a bacterial infection, not a general deficiency of Type 1 muscle fibers, and not due to nutritional atrophy. The specificity to Type 2M fibers explains why the disease is confined to masticatory muscles and why tests often look for autoantibodies against the 2M myosin.