Diagnostic Considerations for Overlap Syndrome

Primary Diagnostic Considerations

The American College of Rheumatology suggests that anti-CCP antibodies are 81-85% specific for Rheumatoid Arthritis (RA) and predict more aggressive disease with structural damage 1
The presence of both high anti-CCP and elevated CRP strongly supports RA diagnosis, as anti-CCP is predictive of RA diagnosis and worse radiographic outcomes, according to the American College of Rheumatology 1
Hand pain with positive anti-CCP is characteristic of RA, even when RF status is unknown, as stated by the American College of Rheumatology 1

Radiographic sclerosis of sacroiliac joints indicates established structural changes consistent with axial Spondyloarthropathy (axSpA), as reported by the American College of Radiology 2, 3
Back pain in a young patient (<45 years) with sacroiliac joint involvement suggests axSpA, according to the American College of Radiology 2, 3

The American College of Rheumatology recommends verifying anti-CCP levels are significantly elevated (>250 U/ml suggests more severe disease) and documenting pattern of joint involvement (small joints of hands/feet typical for RA) 1
Determine if back pain meets inflammatory back pain (IBP) criteria: morning stiffness, improvement with exercise, pain in second half of night, alternating buttock pain, as suggested by the American College of Radiology 2, 3
Order HLA-B27 testing - positive in 90% of axSpA with sensitivity/specificity of 90%, yielding 32% post-test probability, according to the American College of Rheumatology 4

X-rays of hands and feet should be performed at baseline to assess for RA-related erosions, as recommended by the American College of Rheumatology 1
Obtain MRI of sacroiliac joints without contrast if diagnosis unclear, as this is the highest-rated second-line investigation with 79% sensitivity and 89% specificity, according to the American College of Rheumatology 5
Spine radiographs (cervical and lumbar) complement sacroiliac imaging for complete axSpA assessment, as suggested by the American College of Radiology 6

NSAIDs at full dose should be considered for axial symptoms, as good response (within 48 hours) has diagnostic value, according to the American College of Rheumatology 4
Repeat sacroiliac joint X-rays should not be performed more frequently than every 2 years for structural monitoring, as recommended by the American College of Radiology 5, 7