Increased prevalence of scleroderma in southwestern Ontario: a cluster analysis

To estimate the prevalence of scleroderma (systemic sclerosis, SSc) in 3 cities, Windsor, Sarnia, and Woodstock, Ontario, within our referral area, which has a referral base population of 1 million.

To compare the addresses and exposures of referrals with SSc, we performed a case control study using our patients with scleroderma and 2 age and sex matched controls from the same rheumatologist's practice.

Sixty-seven of 91 patients with SSc and 87 of 154 controls responded. The mean age of patients with SSc was 53.2 years versus 52.8 years in controls. There was no statistically significant increase in the number of SSc patients from Windsor (population 197,694): 14 patients (15.4%) with SSc versus 18 controls (11.6%) (p < 0.41); or Sarnia (population 72,738): 7 patients (7.7%) with SSc versus 7 controls (4.5%) (p < 0.31). However, there were 9 cases (9.9%) from Woodstock (population 32,086) versus one control (0.64%) (p < 0.0004). The point prevalence of scleroderma was at least 0.71/10,000 in Windsor, 0.96/10,000 in Sarnia, and 2.8/10,000 in Woodstock. There were no significant between-group differences in exposure to industrial toxins or chemicals including vinyl chloride, silica, and benzene, but exposure rates in both groups were low. Occupations and proportion of those who were work disabled were not different. Patients with SSc were not more likely to have smoked cigarettes (p < 0.43); however, they were more likely to drink at least 6 drinks of alcohol per week (p < 0.04) and had more dental fillings (p < 0.05). Patients with SSc knew on average 3.2 others with this disease, and controls knew only 0.25 others with scleroderma (p < 0.00001). Two patients with SSc knew someone with SSc in their workplace versus none of the controls.

Our a priori expected higher prevalence of scleroderma in Windsor and Sarnia did not reach significance, but the cluster in Woodstock seems statistically validated, and the exact reason for this cluster remains unclear. It is unlikely that all patients with SSc in Woodstock were seen by us, so the prevalence of scleroderma is at least 2.8/10,000, which is a medium to high prevalence compared to other studies. Associations with alcohol and dental fillings require further study.