Myositis ossificans progressiva, left ankle

This code represents a rare, progressive genetic disorder characterized by the abnormal formation of bone in soft tissues, specifically affecting the left ankle. It involves the gradual replacement of muscle, tendons, and ligaments with bone, leading to severe joint stiffness and immobility.

Use this code for patients diagnosed with myositis ossificans progressiva (also known as fibrodysplasia ossificans progressiva or FOP) where the left ankle is the primary or most significantly affected site of heterotopic ossification. Documentation should clearly state the diagnosis of FOP and specify involvement of the left ankle.

• Ensure documentation explicitly identifies "progressiva" to differentiate from localized traumatic myositis ossificans.
• Verify laterality; this code is specific to the left ankle. Use M61.171 for the right ankle or M61.179 for unspecified ankle.
• Consider sequencing this code as a primary diagnosis if the FOP of the left ankle is the reason for the encounter, or as a secondary diagnosis if managing complications related to this condition.