Background Systemic Lupus Erythematosus (SLE) is a rare, autoimmune disease with heterogeneous clinical manifestations. Patients with cutaneous lupus erythematosus (CLE) present with skin rashes without underlying systemic involvement. Few studies have compared the incidence and characteristic of systemic and cutaneous lupus in the same population.

Objectives We estimated and compared the incidence of SLE and CLE from 1993 to 2005, in a population based cohort.

Methods An incident SLE case was defined as an individual who fulfilled four out of 11, 1982 ACR SLE classification criteria and who had been a resident of Olmsted County, MN, USA for at least 1 year prior to first physician diagnosis of SLE (1). Cases with drug induced lupus and overlap diseases were excluded. Cutaneous cases (without systemic features or SLE diagnosis) were identified from a previous data set from 1965-2005 and included patients with classic discoid LE, lupus panniculitis, bullous LE, and subcutaneous LE (2). Overall incidence rates (expressed as per 100 000 population) and 95% confidence intervals (CI) were calculated and age- and sex adjusted to the 2000 US white population.

Results The study included 45 patients with incident SLE and 62 patients with incident CLE in 1993-2005. The overall incidence of SLE and CLE were similar (SLE 2.9, 95% CI 2.0, 3.7 and CLE 4.2, 95% CI 3.1, 5.2, p=0.10). Majority of patients with SLE were female (91% versus 73%, p=0.017). In females, the incidence of both conditions was similar (SLE 5.1, 95% CI 3.5, 6.6 and CLE 5.8, 95% CI 4.1, 7.5; p=0.67). In males, the age-adjusted incidence of SLE was significantly lower than CLE (SLE 0.8, 95% CI 0, 1.6 and CLE 2.4, 95% CI 1.2, 3.6; p=0.009). The mean ages of patients with SLE and CLE were similar (42 years and 47.6 years respectively, p=0.10). The age-specific incidence rates showed that CLE was more common in individuals ≥60 years (9.0) whereas SLE was rare in this age group (2.3). Conversely, CLE was rare in the 20-29 years age group (2.7) compared to SLE (8.0).

Conclusions The overall incidence of CLE and SLE in this population-based study was similar. Cutaneous disease was more common than SLE in males and in older adults which may reflect differences in genetic or environmental etiology of CLE.

References

1. Tan EM, Cohen AS, Fries JF, Masi AT, McShane DJ, Rothfield NF, Schaller JG, Talal N, Winchester RJ. The 1982 revised criteria for the classification of systemic lupus erythematosus. Arthritis Rheum. 1982 Nov;25(11):1271-7.

2. Durosaro, O., M. D. Davis, et al. (2009). Incidence of cutaneous lupus erythematosus, 1965-2005: a population-based study. Archives of dermatology 145(3): 249-253.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.1183