Incidence of rheumatoid nodule in Dalmatia: similarities and differences among populations.

Background: The specific aim of our study was neither prognosis nor long-term evaluation but focus on determining incidence of rheumatoid nodules (RN) in a large population of patients with rheumatoid arthritis (RA) on the coastline of Croatia (Dalmatia) within a certain range. We compared our data with those published previously in the literature.

Methods: Our study was focused on determining incidence of RN occurrence in patients with rheumatoid arthritis in Dalmatia, Croatia by comparing these figures with data reported elsewhere and evaluating its importance in the process of diagnosing RA. The duration of the study was 10 years (1991-2001). There were 421 patients (344 women and 77 men) with confirmed RA diagnosis. Median follow-up time was 2 years (range: 1.4-3.5 years).

Results: Existence of RN was established by clinical examination in 109 of 421 patients; incidence density was 17.3%. RN occurred somewhat more frequently in men (32%) as compared to women (24%) without statistically significant difference. In 38% of patients, RN occurred simultaneously in several sites, more frequently in men (64%) than in women (30%) (odds ratio [OR] 2.13, p <0.05). Correlation of seropositivity and RN appearance was very high: positive in 84% of patients with nodules as compared to 58% of patients without nodules (OR 1.45, p <0.05) with no statistically significant differences between sexes.

Conclusions: Results obtained warrant the conclusion that RN incidence in our patients from Dalmatia is comparable with results of earlier Croatian studies as well as with Western European figures and Caucasian population data reported on other continents. RN incidence differs significantly for Asian and Arabian populations, i.e., is less frequent, and for the U.S. population, where it is more frequent.