HLA-B27 and Back Pain in Psoriatic Arthritis
Yes, patients with PsA frequently have back pain, but HLA-B27 positivity is substantially less common than in ankylosing spondylitis, occurring in only 25-75% of PsA patients with axial involvement compared to 74-89% in AS. 1, 2
HLA-B27 Prevalence in Psoriatic Arthritis
HLA-B27 positivity varies significantly based on the pattern of PsA:
- Axial PsA overall: Approximately 25-75% are HLA-B27 positive, which is notably lower than the 74-89% seen in ankylosing spondylitis 1, 2, 3
- HLA-B27 negative axial PsA (the more common phenotype): These patients present with less inflammatory pain characteristics and less structural damage compared to AS patients with psoriasis 4
- HLA-B27 positive axial PsA: These patients share clinical characteristics more similar to AS, including bilateral sacroiliitis patterns 4
Critical distinction: In one registry study of axial PsA patients, only 30% were HLA-B27 positive 4. Another study found that HLA-B27 and peripheral arthritis act as separate risk factors for spinal involvement in psoriasis patients 5
Back Pain Patterns in PsA
Axial involvement is common in PsA, occurring in approximately 27% of PsA patients: 4
- Inflammatory back pain is present in 70-80% of patients with axial spondyloarthritis overall, characterized by: insidious onset, improvement with exercise, no improvement with rest, occurring at night, and age of onset <40 years 1
- Sacroiliitis patterns differ: PsA typically develops either unilateral or bilateral sacroiliitis, whereas AS characteristically shows bilateral involvement 1
- Peripheral arthritis is more prominent: Patients with psoriatic spondylitis have significantly more peripheral joint involvement compared to AS patients with psoriasis 6
Clinical Implications for Diagnosis
The absence of HLA-B27 does NOT exclude axial PsA:
- Approximately 70% of axial PsA patients are HLA-B27 negative 4
- HLA-B27 negative axial PsA represents a distinct phenotype with different clinical and radiological manifestations 4
- Diagnosis should be based on: combination of psoriasis, inflammatory back pain starting before age 45, peripheral joint pain, and imaging findings—not HLA-B27 alone 2
Referral criteria for suspected axial PsA: Patients with chronic back pain (>3 months) starting before age 45, plus at least 4 of the following should be referred immediately: back pain starting before age 35, current psoriasis, peripheral arthritis, HLA-B27 positive, and likely improvement with NSAIDs or exercise 2
Key Clinical Pitfalls
Common mistakes to avoid:
- Do not rule out axial PsA based on negative HLA-B27 alone, as the majority of axial PsA patients are HLA-B27 negative 4
- Do not assume HLA-B27 positive patients with psoriasis and axial disease have AS rather than PsA—these may represent overlapping phenotypes requiring careful clinical assessment 5, 4
- Do not rely solely on laboratory markers: Normal CRP and ESR do not exclude active axial disease 3
- HLA-B27 testing should be used as a screening parameter to increase pre-test probability, not as a definitive diagnostic test 1, 3
Treatment Response Considerations
Treatment outcomes are similar regardless of HLA-B27 status:
- A 6-month study of biologic/targeted synthetic DMARD therapy showed only mild improvements in axial-related outcomes, irrespective of HLA-B27 status 7
- This reflects a critical unmet need for effective therapies specifically targeting the axial domain of PsA 7
- First-line treatment: Full-dose NSAIDs should be initiated immediately, with 75% of axial spondyloarthritis patients showing good response within 48 hours 2