How to diagnose axial spondyloarthritis early

Abstract

Background: Chronic low back pain (LBP), the leading symptom of ankylosing spondylitis (AS) and undifferentiated axial spondyloarthritis (SpA), precedes the development of radiographic sacroiliitis, sometimes by many years.

Objective: To assign disease probabilities and to develop an algorithm to help in the early diagnosis of axial SpA.

Methods: Axial SpA comprises AS and undifferentiated SpA with predominant axial involvement. Clinical features include inflammatory back pain (IBP), alternating buttock pain, enthesitis, arthritis, dactylitis, acute anterior uveitis, a positive family history, psoriasis, inflammatory bowel disease, and good response to NSAIDs. Associated laboratory findings include raised acute phase reactions, HLA-B27 association, and abnormalities on skeletal imaging. Sensitivities, specificities, and likelihood ratios (LRs) of these parameters were determined from published studies. A 5% prevalence of axial SpA among patients with chronic LBP was used. The probability of the presence of axial SpA, depending on the presence or absence of the above clinical features of SpA, was determined. A probability of > or = 90% was used to make a diagnosis of axial SpA.

Results: The presence of inflammatory back pain features increased the probability of axial SpA from the background 5% prevalence to 14%. The presence of 2-3 SpA features was necessary to increase the probability of axial SpA to 90%. The highest LRs were obtained for HLA-B27 and MRI. Diagnostic algorithms to be used in daily practice were suggested.

Conclusions: This approach can help clinicians to diagnose with a high degree of confidence axial SpA at an early stage in patients with IBP who lack radiographic sacroiliitis.

Figure 1

Decision tree on diagnosing axial SpA. Starting point is the presence or absence of inflammatory back pain (IBP) in patients presenting with chronic back pain. In general, for making the diagnosis of axial SpA a disease probability >90% is suggested. *Dependent on which features are positive (table 2). **If the probability of disease exceeds 90% we consider the diagnosis axial SpA as definite, if the probability is 80–90% we consider the diagnosis as probable (see also "Discussion").

Figure 2

Approach to the diagnosis of axial SpA in daily practice for the physician less experienced (GP) in dealing with patients with rheumatic disease. Percentages in brackets indicate the probability of axial SpA before (pretest probability) and after a test has been performed (post-test probability). *Suspicions for SpA could be the presence of several other clinical features.