Yep. ALL my lab markers were negative, yet my rheumatologist diagnosed enteropathic arthritis based on history and symptoms. If you haven't had x-ray exams of your wrist and knee yet to rule out osteoarthritis and trauma, please get them done. Also, ask your GP to to get lumbar and sacroiliac films, so they can be on file for your rheumatologist. Digital films are best. MRI is not indicated at yhis point.
I was able to take meloxicam and other NSAIDs for years before my pouch acted up. But, the fact that I responded to NSAIDs was more evidence that this was inflammatory in nature.
The not so great news was that the only option open to me were biologics. That was over 10 years ago, and so far, not too much progression. Good luck with your appointment.
Jan