Interstitial myositis, unspecified upper arm

This code signifies an inflammatory condition affecting the muscle tissue within the unspecified upper arm, characterized by the presence of inflammatory cells in the interstitial spaces. It represents a non-infectious inflammation of the muscle fibers, leading to pain, weakness, and swelling in the affected limb.

Apply this code when documentation specifies interstitial myositis affecting the upper arm, but the laterality (left or right) is not explicitly stated. This diagnosis is typically supported by clinical examination findings, muscle biopsy results showing interstitial inflammation, and exclusion of other causes of myositis.

• Ensure the documentation clearly states "interstitial myositis" and specifies the "upper arm" without laterality.
• Avoid using this code if the myositis is due to an infectious agent; instead, code the specific infection.
• If laterality is documented (e.g., left or right upper arm), select the more specific M60.121 or M60.122 code.