Ectopic ossification

As the myositis resolves, the muscle becomes progressively more mineralised.

Ossification preferentially occurs at specific sites:

• in childhood the back and neck are affected, followed by the shoulders and arms
• in adolescence the hips fuse
• as an adult the patient is completely stiff and unable to walk

The following muscles are unaffected:

• the small muscles of the hands and feet
• cardiac and smooth muscle