Objectives: To estimate the incidence of physician-diagnosed primary Sjögren syndrome (SS) among residents of Olmsted County, Minnesota, in the setting of usual medical care and to determine how often objective criteria are available in the medical records of such patients.
Patients and methods: We reviewed all medical records of residents in Olmsted County with physician-diagnosed SS from 1976 to 1992 to determine whether they had undergone objective tests for keratoconjunctivitis sicca, salivary dysfunction, or serologic abnormality. Confounding illnesses were excluded. To identify misclassified cases, all records from patients with xerostomia or keratoconjunctivitis sicca were also reviewed. The average annual SS incidence rates were calculated by considering the entire population to be at risk.
Results: Of 75 patients with onset of SS during the study period, 53 had primary SS. All patients were white, 51 (96.2%) were women, and the mean +/- SD age was 59+/-15.8 years. The age- and sex-adjusted annual incidence was 3.9 per 100,000 population (95% confidence interval, 2.8-4.9) for patients with primary SS. Eleven patients (20.8%) with physician-diagnosed SS had no documentation of objective eye, mouth, or laboratory abnormalities. Objective evaluations performed most frequently were laboratory and ocular tests and least often were investigations of xerostomia.
Conclusions: The average annual incidence rate for physician-diagnosed primary SS in Olmsted County is about 4 cases per 100,000 population. These data probably underestimate the true incidence because they are based on usual medical care of patients with SS in a community setting, rather than on a case-detection survey. In the future, a true incidence may be possible with a higher index of suspicion, greater attention to objective tests, and increased awareness of new classification criteria for SS. For epidemiological studies based on existing data, application of current criteria may not be feasible, and consensus on criteria for such studies would be useful.