Ankylosing Spondylitis: Statement Analysis
Statement (a) is TRUE: Low back pain in AS characteristically worsens with rest and improves with movement—this is the hallmark inflammatory back pain pattern that distinguishes AS from mechanical causes. 1, 2, 3
Detailed Analysis of Each Statement
a) Low Back Pain Pattern: TRUE ✓
The inflammatory back pain in AS demonstrates a pathognomonic pattern:
- Worsens with rest and inactivity (particularly during the second half of the night)
- Improves with exercise and movement
- Associated with morning stiffness
This inflammatory characteristic is fundamental to AS diagnosis and is consistently emphasized across guidelines 1, 2. The ASAS/EULAR recommendations specifically note that pain improves with activity, distinguishing it from mechanical back pain 1.
b) Arthritis Pattern: FALSE ✗
The arthritis in AS is typically symmetric and CAN be erosive, not asymmetric and non-erosive as stated. While AS primarily affects the axial skeleton (spine and sacroiliac joints), peripheral arthritis when present tends toward symmetry. The disease causes structural damage including erosions, syndesmophytes, and eventual fusion 1, 4. The guidelines explicitly discuss radiographic structural damage and erosive changes as part of disease monitoring 1.
c) HLA-B27 Positivity: FALSE ✗
HLA-B27 is positive in approximately 80-90% of AS cases, NOT >90%. While strongly associated with AS, the prevalence varies:
- Research indicates approximately 90% association in some populations 5
- However, HLA-B27-negative AS exists and represents a significant minority 6
- The association is strong but not absolute 7, 8
The statement claiming ">90%" is an overestimate. More accurately, HLA-B27 is present in 80-90% of AS patients, with variation by ethnicity and population 5, 7, 6.
d) Kidney Involvement: FALSE ✗
Kidney involvement is NOT common in AS. The guidelines consistently identify extra-articular manifestations as:
- Acute anterior uveitis (most common)
- Inflammatory bowel disease
- Psoriasis
- Aortitis/carditis
Renal involvement is not listed among the characteristic extra-articular features in any of the major guidelines 1, 9, 10, 2. The ASAS core set for disease monitoring specifically mentions uveitis, conjunctivitis, and carditis—but not kidney disease 1.
e) Antinuclear Antibodies: FALSE ✗
ANAs are NOT always positive in AS—in fact, AS is classified as a seronegative spondyloarthropathy. The evidence shows:
- ANAs found in only 19.1% of AS patients in one study 11
- AS is characterized by the absence of rheumatoid factor and typically negative autoantibodies
- The term "seronegative spondyloarthritis" specifically denotes the lack of typical autoantibodies 5, 4
The frequent co-testing of HLA-B27 with ANA and rheumatoid factor (69.3% of cases) 12 represents inappropriate testing patterns, not disease characteristics.
Clinical Pitfalls to Avoid
- Don't dismiss AS based on negative HLA-B27: 10-20% of AS patients are HLA-B27 negative 6
- Don't confuse AS with rheumatoid arthritis: AS is seronegative; routine ANA/RF testing is not indicated 12
- Don't overlook the characteristic pain pattern: Improvement with exercise is key to diagnosis 2, 3
- Don't expect renal involvement: Focus on uveitis, IBD, and cardiac manifestations instead 1, 2
CORRECT ANSWER: Only statement (a) is true.