Coexisting rheumatoid arthritis and ankylosing spondylitis

Area of Science:

• Rheumatology
• Immunogenetics

Background:

• Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are distinct autoimmune diseases.
• Coexistence of RA and AS in a single patient is rare and may be underdiagnosed.

Observation:

• Seven new cases of coexisting RA and AS were identified, adding to a previous cohort for a total of 17 patients.
• The cohort comprised 13 males and 4 females, with all patients testing positive for rheumatoid factor.
• Six patients presented with subcutaneous nodules, a feature more common in RA.

Findings:

• A significant association was observed between the coexisting conditions and specific genetic markers.
• The antigen HLA-DR4 was present in 8 of 12 tested patients.
• The antigen HLA-B27 was present in 16 of 17 patients, a marker strongly associated with AS.

Implications:

• The findings suggest that the co-occurrence of RA and AS is likely coincidental rather than pathogenically linked.
• The high prevalence of HLA-B27 supports the strong genetic predisposition to AS even when RA is also present.
• Clinicians should consider the possibility of coexisting RA and AS, especially in patients with positive rheumatoid factor and relevant genetic markers.