Dual seropositive nonerosive lupus arthritis: rhupus or not?

There is no consensus on the classification of lupus arthritis (LA). In this study, we aimed to investigate patients with LA who were clinically and serologically very similar to those patients with rheumatoid arthritis (RA).

The electronic medical files of systemic lupus erythematosus (SLE) patients from a single tertiary rheumatology department between 2017 and 2022 were reviewed. The inclusion criteria were being age ≥ 18 years, having nonerosive peripheral arthritis lasting longer than six months, and having dual seropositive (rheumatoid factor (RF) and anti-citrullinated protein antibody (anti-CCP)) serology. A nonerosive course of arthritis was demonstrated by both conventional radiography and joint ultrasound. Images were assessed by two blinded rheumatologists. Patients with drug-induced lupus and those with other rheumatologic diseases were excluded.

The cases of 528 patients were reviewed, and eight patients were included in the study. All patients were female, and the median age was 48.5 years. The median SLE and arthritis durations were 12 and seven years, respectively. The most common SLE symptom was photosensitivity (n = 8). Only one patient had life-threatening involvement (LTI), which was a seizure and autoimmune haemolytic anaemia. All patients had arthritis affecting the wrist and hand. Anti-dsDNA was the most common anti-ENA antibody (n = 7), followed by anti-SSA (n = 5). The median RF and anti-CCP titres were 82.5 IU/ml and 81.5 U/ml, respectively. Five patients had high titres of autoantibodies, and only one patient had slight hypocomplementemia. Three patients needed biologic agents, and remission was achieved after treatment with rituximab.

Despite a long arthritis duration and dual seropositive serology with high titres of RF and anti-CCP, our patients had SLE rather than rhupus syndrome. The low frequency of LTIs, such as lupus nephritis, was a remarkable feature of our patients. Lupus arthritis may be clinically and serologically indistinguishable from RA. Prospective studies are needed to better define LA.