Rhupus syndrome: a unique disease overlapping systemic lupus erythematosus and rheumatoid arthritis

Background though considered to have characteristics of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) theoretically, Rhupus Syndrome (RS) owns its unique clinical features. In this retrospective cross-sectional study, we included 41 newly diagnosed Rhupus syndrome patients (NRSP). 160 new-diagnosed systemic lupus erythematosus patients (NSLEP) and 709 new-diagnosed rheumatoid arthritis patients (NRAP) were admitted as positive control groups. The clinical, serological, and radiological features among groups were compared, the disease activity of RA and SLE was evaluated, and the proportion of lymphocyte subsets in NRSPs under similar disease activity levels was explored. The initial onset age of RS patients was significantly younger than RA patients (P = 0.032), older than SLE patients (P = 0.008). 19.5% (8/41) RS patients initially presented with SLE symptom, while 12.2% RS patients presented with symptoms of both diseases. Hematopoietic dysfunction was the most prominent systemic manifestation in RS (61.0%, 25/41), only 9.8% patients experienced renal damage, and neurological disease were even rarer. Moreover, RS exhibited immunological characteristics different from NRAPs and NSLEPs, mainly manifested in decreased CD4⁺ T cell and NK cell counts, increased ratio of CD8 + T (%) and total B cells, and decreased ratio of NK cells. RS is characterized by a higher incidence of interstitial lung disease and significant hyperglobulinemia besides the typical clinical characteristics of RA and SLE, which may be associated with a re-imbalanced lymphocyte subset. Evaluation of disease activity of RS cannot only rely on either SLEDAI-2 K or DAS28-ESR/-CRP, but more comprehensive assessment tools.