Polyarthritis is a form of arthritis which affects 5 or more joints simultaneously. It is usually associated with other autoimmune conditions such as psoriasis, colitis and crohns. Subcategories include Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), Seronegative Arthritis and Psoriatic Arthritis.
RA is a symmetrical arthritis that affects multiple synovial lined joints. It is characterised by progressive articular damage leading eventually to joint deformation. RA was initially thought to be associated with HLA-DR4 but is now seen to be more associated with a set of shared epitopes in positions 70-74 of the HLA-DRB1 locus. The epitopes include the amino acid sequences QKRAA, QRRAA, RKRAA AND RRRAA. HLA class II alleles which share these epitopes include HLA-DRB1*01:01, *01:02, *04:01, *04:04 and *04:05. Alleles which do not share these epitopes and which may be protective for RA include HLA-DRB1*03 and HLA-DRB1*04:03.
SLE is an arthritic condition characterised be repeated bouts of relapse and remission of symptoms including pain. It is associated with production of anti-nuclear autoantibodies, including anti-Sm, anti-Ro/SSA and anti-La/SSB. Presence of anti-Ro/SSA and anti-La/SSB autoantibodies is associated with the HLA class II DRB1*03:01 allele. Presence of anti-Sm autoantibodies is associated with the HLA class II DRB1*15:01 allele.
Seronegative Arthritis describes a set of arthritic conditions all of which are characterised by absence of rheumatoid factor (rheumatoid factor is an autoantibody against the Fc portion of IgG). These include the seronegative spondyloarthropathies and seronegative Rheumatoid Arthritis. Seronegative Polyarthritis is in some cases associated with other systemic autoimmune diseases including psoriasis, bowel and bladder symptoms and anterior Uveitis all of which have different HLA associations. The seronegative spondyloarthropathies are associated with HLA-B27. Uveitis is also associated with HLA-B27, while Behcet’s is associated with HLA-B51. Seronegative Rheumatoid Arthritis may be associated with HLA-DR4.
Psoriatic Arthritis is an inflammatory joint disease which is associated with a psoriatic rash and swelling of the fingers (Dactylitis). Symptoms include spinal pain and enthesitis. Anterior Uveitis is seen in about a third of cases, though symptoms are often temporary. Nail involvement is common. HLA types implicated in susceptibility to Psoriatic Arthritis include HLA-B*27, HLA-B*39 and HLA-C*06:02.
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