What causes neck arthritis is a young adult? my mri showed narrowing of the disc space and a slight bulge.

Incidental finding: Up to 15% of people under 40 have MRI evidence of degenerative changes. What was the reason your physician ordered the mri? What were your symptoms?

Trauma, arthritis: Trauma and inflammatory arthritis can cause neck arthritis and the disk change are of concern, but the bulge is unlikely to be causing the pain. Evaluation for fibromyalgia and position-related strain would be worthwhile.