I’m HLA-B27 negative and my rheumatologist said ALL my blood tests and urinalysis are normal. My X-rays also look normal, with the exception of lordosis reversal and mild arthritis in SI joints. I'm a 37 y/o male.

However, my rheumatologist diagnosed me with AS due to the following:

-Diffuse inflammation (knee, thumb, big toe, wrist, and most importantly, SI joint)
-Complaint of lower back pain
-Mild arthritis of SI joints on x-rays
-Reversal of lordosis

Given that I have normal blood/urine tests and am antigen negative, I’m looking for insight on:
-Whether this could actually be something else?
-Any treatments that are particularly effective/ineffective for this type of AS?
-Any other insights into how this AS type is different from someone with abnormal blood tests and antigen positive

Thanks so much for your help!