Clinical features and race-specific incidence/prevalence rates of systemic lupus erythematosus in a geographically complete cohort of patients.

To assess race-specific incidence and prevalence rates for systemic lupus erythematosus (SLE) using 1991 National Census data and to ascertain the frequency of clinical/laboratory features of a geographically complete cohort of patients with SLE. Multiple methods of retrieval were used to ascertain SLE patients including screening request cards for immunology investigations. Patients were classified according to the revised ARA criteria. Multiple logistic regression analysis was used to study the effects of age at diagnosis on the frequency of clinical/laboratory SLE features. The overall one year period prevalence rate for SLE was 24.7 (age adjusted, 95% CI: 20.7-28.8)/100,000. Highest rates were seen in Afro-Caribbeans (207 (111-302)/100,000), followed by Asians (48.8 (10.5-87.1)/100,000), and then Whites (20.3 (16.6-24.0)/100,000). The mean age at diagnosis of SLE was 40.9 years (range: 11-83) with a mean interval between first definite SLE symptom and diagnosis of 61 months (0-518). In 85% of patients the first definite lupus feature was musculoskeletal and/or cutaneous. In this SLE cohort renal disease (22%) was observed less commonly than in previous studies and the 'classic' butterfly rash was present in only 30% of patients. Malar rash, thrombocytopaenia, positive anti-dsDNA antibodies, hypocomplementaemia (C4), and positive IgG anticardiolipin antibodies were all seen less commonly with increasing age at diagnosis. A closer estimate of the true frequency of clinical/laboratory SLE manifestations is likely from this geographically complete cohort of patients compared with studies that may be skewed by referral patterns.