M60: Myositis

M60.1: Interstitial myositis

Interstitial myositis is a medical condition characterized by inflammation within the muscles, specifically between the muscle fibers. It is a type of myopathy – an umbrella term for diseases affecting the muscle tissues. Though the exact cause of interstitial myositis is unknown, it is often the body’s immune response reacting abnormally. This immune reaction results in swelling and damage to the muscle tissues. Common symptoms can include muscle weakness, muscle pain, fatigue, and trouble with physical tasks that were once easy, like climbing stairs. The disease can progress over time, leading to a gradual decrease in muscle strength and functionality. It can affect any muscle group in the body, but it most commonly impacts muscles close to the center of the body, such as those in the hips, thighs, shoulders, or upper arms.