Canine Masticatory Muscle Myositis Study Guide

Overview and Clinical Importance

Masticatory Muscle Myositis (MMM) is an immune-mediated inflammatory myopathy that selectively affects the muscles of mastication in dogs. It is the most common focal inflammatory myopathy in dogs and represents a significant topic for NAVLE examination due to its unique pathophysiology, distinctive clinical presentation, and specific diagnostic approach.

MMM is characterized by autoantibodies directed against type 2M muscle fibers, which are unique to the masticatory muscles. This specificity provides the basis for both the selective muscle involvement and the highly specific diagnostic test. Early recognition and aggressive immunosuppressive therapy are critical for optimal outcomes.

Anatomy of the Masticatory Muscles

The muscles of mastication are the group of muscles responsible for jaw movement during chewing. They are all innervated by the mandibular branch of the trigeminal nerve (CN V). This shared innervation is significant because the masticatory muscles contain a unique myosin isoform (type 2M fibers) that is not present in other skeletal muscles.