The influence of thyroid diseases, diabetes mellitus, primary hyperparathyroidism, vitamin B12 deficiency and other comorbid autoimmune diseases on treatment outcome in patients with rheumatoid arthritis: An exploratory cohort study

To investigate the impact of comorbid diseases on rheumatoid arthritis (RA) outcome. All patients diagnosed with RA since 2006, who were registered in our local Danbio registry, were included in this cohort study. Patients’ demographics, serology results, and Disease Activity Score in 28 joints-C-reactive protein (DAS28-CRP) at the time of diagnosis and after 4 months of treatment initiation were collected. Patients’ electronic hospital records were evaluated for a positive history of thyroid diseases, diabetes mellitus, primary hyperparathyroidism, vitamin B12 deficiency, and the presence of other diagnosed autoimmune diseases. 1035 RA patients were included. The observed prevalence of thyroid diseases was 11.8%, DM 10.4%, primary hyperparathyroidism 2.8%, vitamin B12 deficiency 5.8%, and other diagnosed autoimmune diseases 1.6%. There were significant associations between presence of thyroid diseases and female gender (P < .001); DM and greater age (P < .001); primary hyperparathyroidism and longer disease duration (P = .002); other diagnosed autoimmune diseases and antinuclear antibody positivity (P < .001). RA patients with thyroid diseases (P = .001) and other comorbid autoimmune diseases (P < .001) had significantly poorer initial response to the RA treatment compared to patients with isolated RA. Univariate analyses revealed that age, the presence of thyroid diseases, the presence of other diagnosed autoimmune diseases and DAS28-CRP at the time of diagnosis were significantly associated with ΔDAS28-CRP. Additionally, multivariate analysis demonstrated that ΔDAS28-CRP deterioration was significantly correlated to the presence of thyroid diseases (unstandardized regression coefficient (standard error); −0.188 (0.088), P = .030) and the presence of other diagnosed autoimmune diseases (−0.537 (0.208), P = .010). RA patients are at increased risk of specific comorbidities with possible impact on the treatment outcome. To improve this situation, periodic assessment of comorbidities should be considered.