Orbital myositis, bilateral

This code describes inflammation of the extraocular muscles affecting both eyes. Orbital myositis is an idiopathic inflammatory condition that can cause pain, proptosis, diplopia, and restricted eye movement. It is a form of idiopathic orbital inflammation (IOI).

Apply this code when documentation clearly indicates bilateral involvement of the extraocular muscles due to inflammation. This diagnosis is typically made based on clinical presentation, imaging studies (e.g., MRI or CT showing enlarged extraocular muscles), and exclusion of other causes of orbital inflammation.

• Ensure documentation specifies "bilateral" involvement; otherwise, a unilateral code (H05.121 or H05.122) or unspecified code (H05.129) may be more appropriate.
• Distinguish from thyroid-associated orbitopathy (TAO), which also causes extraocular muscle enlargement but has a different etiology and specific codes (e.g., H06.2-).
• Code any associated symptoms (e.g., diplopia, proptosis) separately if documented and not inherent to the myositis.