INCIDENCE OF SYSTEMIC CONNECTIVE-TISSUE DISEASES IN CHILDREN - A NATIONWIDE PROSPECTIVE-STUDY IN FINLAND

Objective. To study the incidence of systemic connective tissue diseas es (CTD) and of systemic onset juvenile arthritis (S-JA) in children a ged 0 to 15 years. Methods. A nationwide, prospective, hospital based series of new patients from Finland collected during a 4-year period a nd supplemented with data from the National Hospital Discharge Registe r. The population at risk was 1.02 million. Classification criteria de veloped for adult CTD and the American Rheumatism Association criteria for JA were used. Results. The annual incidence rates found were as f ollows: systemic lupus erythematosus 0.37, poly myositis/dermatomyosit is (PM/DM) 0.30, mixed connective tissue disease 0.10, scleroderma 0.0 5, and S-JA 0.47/100,000. Girls outnumbered boys in the whole series o f CTD (24:9) and also in S-JA (11:8), but in PM/DM the sex distributio n was even. Conclusion. CTD and S-JA are rare before the age of 16 yea rs. From the present incidence figures and those recently published fo r JA the incidence of CTD is estimated to be between 4 and 7% of that of JA, and S-JA accounts for only 2 to 4% of all JA.