To the Editor:
The report by Christiansen, et al1 again emphasizes one of the limitations to clinical application of our diagnostic paradigms. Sacroiliac joints (SIJ) have highly irregular contours with 3-D topography2. Imaging artifacts related to the limited resolution of computed tomography (related to the subchondral bone thickness of SIJ) compromises its reliability in identifying or excluding not only erosions, but also bridging or fusion3,4. Standard radiographs also have limited resolution, but no averaging artifact. One would anticipate that they would provide clarity, and they generally do for most joints. SIJ are an exception1,3. The irregular characteristic of the joint and its positioning outside of visualization on standard anterior-posterior and lateral views are thought responsible for erroneous perspectives of the “health” of the joint5. However, experimentation with alternative views (Table 1) failed to provide a solution3.
Radiologic views for sacroiliac joint visualization3.
The category of disease inclusive of ankylosing spondylitis (AS) and spondyloarthropathy (SpA) in general is a construct. Clinical, laboratory, and radiologic findings have been used to facilitate its recognition. However, it is perhaps useful to examine the clinical purpose of categorization. Is it not to define a clinical population that would be anticipated to respond to a specific course of treatment?
Back pain that is worse with immobility, improved with activity, and associated with significant morning stiffness is highly characteristic, although arguably not definitive for the diagnosis of AS or at least the axial presentation of SpA6. If radiologic findings are not always reliable1,3, the value of HLA-B27 positivity is limited by its high presence in healthy individuals7, and acute-phase reactants are variable8, is therapeutic response an alternative diagnostic consideration? If the patient’s pain complaints respond to an extension exercise program (with avoidance of flexion activities), the diagnosis of SpA is highly likely9. After all, we are clinicians and from a clinical perspective, the patient’s problem has been resolved.
