"Back pain, enthesitis, and peripheral arthritis are common, as well as extra-skeletal manifestations such as dactylitis and fatigue 1."
"Only 50% of presentations have abnormal levels of acute-phase reactants (CRP, ESR), and only 10% are positive for rheumatoid factor despite many eventually declaring themselves as rheumatoid arthritis 3."
"Undifferentiated spondyloarthritis (uSpA), also known as undifferentiated arthritis, is a non-specific mono- or polyarthropathy that lacks the clinical, serological and radiological features that would allow specific diagnosis. It often turns out to be an early presentation of a more well-known form of arthritis."