Allen E et al. (2006) A statistical analysis of the interrelationships between disease activity in different systems in systemic lupus erythematosus. Rheumatology 45: 308–313

Patients with systemic lupus erythematosus (SLE) tend to present with multisystem disease, or symptoms that focus on the renal or the musculoskeletal and mucocutaneous systems. This pattern of presentation has led some clinicians to believe that distinct subtypes of SLE exist, so Allen et al. performed a statistical analysis to examine the relationship between renal, musculoskeletal, and mucocutaneous disease activity.

The team prospectively collected data on 440 patients from two Birmingham, UK hospitals over a 10-year period. Sociodemographic data were obtained at the first visit and disease activity (measured by the BRITISH ISLES LUPUS ASSESSMENT GROUP [BILAG] INDEX) and medication usage were recorded at every clinic visit (median time between visits 90 days). Organ damage was assessed every 6 months.

They found that, in the three systems studied, patients with a higher frequency of clinic visits with active disease were more likely to continue with active disease in that system (and not in any other), compared with patients who had a lower frequency of visits. In addition, they found that renal disease is most likely to occur on its own, but that patients with predominantly mucocutaneous symptoms might develop musculoskeletal symptoms, and vice versa.

These findings were validated in a second cohort of 295 patients from a different UK hospital; similar relationships were seen, indicating that patients with renal symptoms, and patients with mucocutaneous and musculoskeletal symptoms, respectively, might represent distinct subgroups of SLE patients.