Hello, Miranda:
The mri and even X-rays are not very effective at finding the inflammation so characteristic of AS; nuclear bone scans are much better, but still not fully reliable.
The thing is, YOU know where You hurt and this pain is NOT due to direct injury; it is obviously inflammation.
Regret the HLA B27 serological test is not very reliable, either; Fc or ELISA should be de rigueur (IMHO), especially for women with symptoms.
It is a painful situation because many women, despite the pain from inflammation, might never fuse; it has been suggested that, overall, the protracted pain and frustration of being mislabeled (fibromyalgia is the most common misdiangosis), women with AS have a much tougher time than men. Regret the bias against getting a proper diagnosis for women.
AS is so individualistic that even an answer to the question "how long to damage?" cannot be relied upon and especially for women. For men this disease has very common traits and symptom progression; much less so in women due to many specific gender-related factors.
For the B27 positive person, Professor Ebringer has offered six definitive symptoms for diagnosis of "Pre-AS" but I wanted to expand upon this, and this information may be of help to You in "nuancing" a diagnosis. If interested, please check out my "Important AS Resources" link in my signature below; there is a diagnostic page.
HEALTH,
John
