Background/Purpose: Palindromic rheumatism (PR) may evolve to rheumatoid arthritis (RA), particularly in patients with citrullinated peptide/protein antibodies (ACPA), although a significant number of patients do not progress to RA in the long term. Differences in ACPA specificities have been shown between patients with established and preclinical RA. It is unclear whether ACPA specificities differ between patients with longstanding PR and RA. To determine whether there are differences in the recognition of epitopes between patients with longstanding PR and established RA by analysis of different ACPA specificities.

Methods: Case-control study. Cases: patients with pure PR, with no evolution to RA or other rheumatic disease at study entry. Controls: patients with established RA (ACR-87) matched by sex, disease duration and ACPA positivity (commercial CCP2 test [Eurodiagnostica]; NV<50U). ACPA specificity in sera was determined by ELISA test using a synthetic citrullinated peptide of fibrin as antigen: [Cit ⁶³⁰] α-Fibrin (617-631)(p18), two peptides of vimentin ([Cit ⁷¹] Vim (47-72)(p48), [Cit ^64,69,71] Vim (47-72)(p55)) and one peptide of α-enolase: [Cys^4,22 , Cit ^9,15] Enolase (5-21)(CEP-1). The cut off for each ELISA test was established by ROC curves, with a specificity of 98% compared to a healthy population (blood donors, n=64). The presence and number of different ACPA specificities in the two groups was analyzed.

Results: We included 108 patients: 54 PR and 54 RA. 62.9% were female and 66.7% in both groups were CCP2 positive. No significant differences between groups in mean age (51.2±11.3 y vs 54.7±11.8 years) and disease duration (11.6±10.7 y vs. 8.3±6.1 years) were found. PR patients had a lower frequency of some ACPA specificities than RA, which was significant in the case of p 48 vimentin (1.9% RP vs. 14.8% AR, p: 0.015) and, especially, p 55 vimentin (PR 24.1% vs. 59.3% RA, p: <0.001). The mean number of ACPA specificities was lower in PR than in RA patients (0.9±0.9 PR vs. 1.4±1.03 AR, p=0.008). The percentage of sera with no ACPA specificity was greater in PR than in RA patients (42.6% vs 22.2% p= 0.02) (see Table). No differences between groups in the levels of different ACPA specificities were observed.

Conclusion: Patients with PR had a lower frequency of some antigenic specificities of ACPA in comparison with RA patients, especially in the case of citrullinated vimentin. PR patients also had a lower total number of specificities than RA patients. PR patients with fewer ACPA specificities and no recognition of citrullinated vimentin may have a better prognosis, without progression to RA.

Table: ACPA specificities in patients with PR and RA

	PR n=54	RA n=54	p
CCP2, n,%	36 (66.7)	36 (66.7)	1
CCP2, levels	392.6 ± 527.6	487.4 ± 584.4	0.37
p18 α-fibrin n, %	19 (35.2)	26 (48.1)	0.17
CEP-1 enolase n, %	16 (29.6)	21 (38.9)	0.31
p48 vimentin n, %	1 (1.9)	8 (14.8)	0.015
p55 vimentin n, %	13 (24.1	32 (59.3)	‹0.001
Number of Vimentin specificities, mean	0.26 ± 0.4	0.74 ± 0.7	‹0.001
Total number of ACPA specifies	0.91 ± 0.96 (min 0 – max 3)	1.43 ± 1.03 (min 0 – max 3)	0.008
Total number of ACPA specificites  0 1 2 ≥2	23 (42.6) 17 (31.5) 10 (18.5) 14 (25.9)	12 (22.2) 17 (31.5) 15 (27.8) 25 (46.3)	0.024 1 0.25 0.028

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differing-specificities-of-anticitrullinated-peptideprotein-antibodies-in-palindromic-rheumatism-and-rheumatoid-arthritis-a-case-control-study/