Discussion
The prevalence of JA in this cohort was low (1.1%) when compared with the frequencies reported in other studies1 2 4 where the ranges varied between 2% and 5%. This could be due to the recent diagnosis of SLE and to the relatively short follow-up time of the members of this cohort. The majority of the authors agree that JA is a relatively late SLE manifestation, although other authors propose that JA could be an early disease manifestation.4 8 The dissimilar frequencies observed in the studies alluded to may relate to inclusion bias1–4 9 and the definition of JA used by different authors. In fact, a clear-cut definition of deforming arthropathy in SLE has not been well accepted or developed; the classification criteria can be clinical (any deviation of the metacarpal finger axes assessed by a goniometer), as described by Alarcón-Segovia et al4 or using the diagnostic index developed by Spronk et al,8 which allows for the presence of different deformities, and attributing JA a score of over 5 points; however, van Vugt et al2 added the presence of erosions in hand and feet radiographs. Thus, patients may have an erosive arthropathy (EA), which several authors have called it Rhupus2 8 or, in the absence of erosions on hand radiographs, definitive JA or mild deforming arthropathy (MDA), depending on the score values.
The aetiopathogenesis of JA is not at all clear; several theories have been postulated: hypermobility of the joints, hyperparathyroidism secondary to renal failure, in advanced stages of the disease, and consequently tendinous laxity, as well as the persistence of mild joint inflammation.1 2 10
Many authors claim that persistent inflammation and small erosions may be under diagnosed on radiographs but can be detected on ultrasound (US) or on MRI.11–13 Sá Ribeiro et al13 studied 20 patients with SLE with JA and more than 300 joints were evaluated by MRI. Synovitis was observed in 67.3%, tenosynovitis in 38.5% and in 5.3% in small areas of erosions. Similarly, Lins et al14 examined 40 patients and 560 joints by US; 47.5% had synovial hypertrophy, 22.5% had tenosynovitis and 5.0% small erosions; there was no association between these findings and disease activity (p=0.33).
Within the clinical features, lupus pneumonitis was found more frequently among the patients with JA than those without it; however, the CI was wide, and thus, this finding needs to be interpreted with caution. We did not find a higher frequency of renal manifestation among our patients with JA. Van Vugt et al2 described a negative association between the presence of JA and lupus nephritis. This apparent protective effect could not be corroborated by Lhakum et al15; they studied 458 patients with SLE; deforming arthropathy was present in 40 of them (8.7%). The prevalence of EA, JA and MDA was 2.8%, 1.8% and 4.1%, respectively. In this study, a higher occurrence of renal involvement (69.2%) as well as another major organ involvement, particularly neurological and haematological, was found among the patients with JA.
We found no specific relationship between JA and any autoantibodies including anti-SSA/Ro, SSB/La and antiphospholipid antibodies. These last have even been postulated as part of pathophysiology, with microvascular damage.4 5 Likewise, JA does not appear to have a direct impact on either disease activity, damage accrual or survival in our cohort.
Our study has some limitations. First, the small number of individuals identified precludes us from making definitive conclusions about our findings; second, although investigators participating in the GLADEL cohort were trained in data collection prior to study initiation, it is possible that JA may have not been detected by some of them; furthermore, the lack of more refined methods to evaluate erosions makes it possible that some patients may have been misclassified; third, data on rheumatoid factor and anticyclic citrullinated peptide, as well as, acute phase reactants and auto antibodies were not systematically obtained in our patients; and fourth, the association between JA and pneumonitis needs to be interpreted with caution given its wide CI.
Despite these limitations, we can conclude that JA could be considered a manifestation that may appear early in the course of SLE and associated with certain clinical features (pulmonary involvement) but apparently has no impact on either disease activity, damage accrual or survival.