HLA-B27-positive oligarthritis.

68 cases with polyarthritis were selected from 406 HLA B 27 positive patients with various rheumatic diseases excluding ankylosing spondylitis (AS) or Reiter's disease. 23 fulfilled at least 5 criteria of the ARA for the diagnosis of rheumatoid arthritis (RA). 5 suffered from polyarthritis and psoriasis. The remaining 40 patients expressed an asymmetric oligarthritis especially of the lower limbs (knee, ankle) affecting predominantly young adult men. Sacroiliitis was observed in 10 cases. Joint erosions, rheumatoid factors and visceral manifestations were uncommon. The arthritic pattern of B 27 positive oligarthritis differed clearly from rheumatoid arthritis (n = 34) and psoriatic arthritis (n = 15), but was similar to peripheral joint involvement in AS (n = 32) except for the higher incidence of coxitis in AS. HLA typing is helpful not only in the early diagnosis of AS but also in the differential diagnosis of unclassifiable polyarthritis.