Interstitial myositis, multiple sites

This code signifies an inflammatory condition affecting the interstitial connective tissue within multiple muscles, not limited to a single anatomical region. It represents a diffuse form of myositis where the inflammation is primarily located in the spaces between muscle fibers rather than the fibers themselves.

Use this code when documentation clearly indicates interstitial myositis affecting more than one distinct muscle group or anatomical site. This diagnosis is typically supported by muscle biopsy findings, imaging studies (e.g., MRI), and clinical presentation of widespread muscle pain, weakness, and elevated inflammatory markers.

• Ensure documentation specifies "multiple sites" or lists several affected muscle groups to justify this code over a site-specific myositis.
• Distinguish from other forms of myositis (e.g., polymyositis, dermatomyositis) which have their own specific codes.
• Code any associated underlying systemic conditions (e.g., autoimmune diseases) as primary diagnoses if they are the cause of the interstitial myositis.