Silica exposure in anti-neutrophil cytoplasmic autoantibody-associated glomerulonephritis and lupus nephritis

Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated small-vessel vas culitis (SVV) and systemic lupus erythematosus (SLE) are rare diseases with unknown causes. Silica dust exposure has been suggested to be an environme ntal factor that may increase the risk of developing these and other autoim mune disorders. This is a report of two case-control studies to determine w hether silica dust exposure is independently associated with ANCA-SVV with glomerulonephritis and SLE nephritis. Patients were screened through a coll aborative network of 225 private practice and university nephrologists (the Glomerular Disease Collaborative Network). Patients with ANCA-SVV or SLE, all with biopsy-proven renal involvement, were included. Control subjects w ere patients without ANCA-SVV or SLE who had been referred to the same rena l clinics and were matched for gender, race, and age (within 5 yr). Exposur es to silica, exposures to other environmental agents, and smoking historie s were evaluated using a self-administered questionnaire. Enrollment consis ted of 65 patients with ANCA-SVV and 51 patients with SLE nephritis. Silica dust exposure was reported by 46% of patients with ANCA-SVV, compared with 20% of control subjects (P = 0.001). The odds ratio of silica dust exposur e was 4.4 times greater for patients with ANCA-SVV, compared with control s ubjects (95% confidence interval, 1.36 to 13.4; P = 0.013). The odds ratios for silica dust exposure were similar for patients with ANCA-SVV with lung or sinus vasculitis (odds ratio, 4.5; 95% confidence interval, 0.99 to 20. 83; P = 0.054) and those without lung or sinus vasculitis (odds ratio, 4.7; 95% confidence interval, 1.34 to 16.24; P = 0.016). Silica dust exposure w as reported by 12% of patients with SLE nephritis, compared with 25% of con trol subjects (P = 0.047). The odds ratio for exposure to silica dust was n ot statistically different for patients with SLE nephritis, compared with c ontrol subjects (odds ratio, 0.001; 95% confidence interval, <0.01 to >100; P = 0.993). Activities and environments known to cause high levels of expo sure to silica dust were associated with ANCA-SVV but not with SLE nephriti s.