Background RA has been viewed for many years as a heterogeneous collection of rheumatic diseases. Previously rheumatoid factor (RF) positive and negative patients were regarded as distinct clinical subtypes. Additionally, within seropositive RA those with very strongly positive RF levels were also thought to have a characteristic disease process. The addition of anti-citrullinated protein antibody (ACPA) testing has led to a distinction between ACPA positive and negative patients. However, no studies have compared the clinical presentation of RA patients with very strongly positive ACPA levels associated with a negative or low-positive RF levels with those RA patients with a very strongly positive RF.
Objectives To assess the clinical presentation and demographics of RA patients with very strongly positive ACPA levels (>170 IU) in the presence of a negative or low-positive RF (≤30 IU) compared to patients with a very strongly positive RF (>300 IU).
Methods The study included 64 RA patients with a disease duration 170 IU) was present in 22 patients, this group will be referred to as the discordant antibody group. 42 had very strongly positive RF levels (arbitrarily 10 fold higher than the upper normal range 0-30, i.e. >300 IU). Data was collected through analysis of clinic letters and a serologically blinded telephone questionnaire. Patients with a personal or family history of psoriasis were excluded.
Results Demographics: There was a significantly increased prevalence of females in the discordant antibody group (82% vs. 45%) p=0.005
Clinical features: Palindromic rheumatism was significantly more likely to precede the diagnosis of RA in the discordant antibody group (8 of 22 (36%)) compared to the strongly positive RF group (1 of 42 (2%)) p=0.0009. An asymmetrical onset was significantly more likely in the discordant antibodies group (15 of 22 (68%) vs. 14 of 42 (33%)) p=0.008. There was a significantly increased prevalence of large joint† involvement in the discordant antibody group (16 of 22 (72%) vs. 15 of 42 (35%)) p=0.005.The presence of nodules and PMR presentation did not differ significantly between the two groups p=0.22.
† Large and small joints were defined according to 2010 ACR-EULAR criteria.
Conclusions Patients with very strongly positive ACPA levels associated with a negative or low-positive RF levels were significantly more likely to be female and to have a palindromic type presentation. Large joint and an asymmetrical presentation were also significantly more prevalent in this group and further studies are required to determine whether this group are a new and distinct subtype of RA.
Disclosure of Interest None Declared