Risk of comorbidities in patients diagnosed with chronic urticaria: A nationwide registry-study

BACKGROUND: The autoimmune profile of Chronic Urticaria (CU) patients is an increasing topic of interest. Associated diseases suggest shared pathogenic pathways, and they may provide important knowledge on specific targets for future treatment models. In this study we examined the prevalence and risk of comorbidities in CU. METHODS: The Danish National Patient Registry was used to identify all CU patients from 1994 to 2015. Five of 5 specialized dermatological units in Denmark were covered. Analyses were conducted as a nested case control study and a matched cohort study. CSU patients were matched 1:10 on age and sex to an otherwise random group of people from the background population. RESULTS: A total of 12,185 CU patients were identified, with an overweight of female cases (69% versus 32%). There was an overrepresentation of mast cell mediated diseases including mastocytosis and anaphylaxis, as well as atopic diseases including type 1 allergies and atopic dermatitis. The prevalence of rheumatoid arthritis, systemic lupus erythematosus, thyroiditis and vitiligo was also increased, as was the prevalence of depression. CU patients who did not have any of the co-morbidities at the time of their CU diagnosis had an increased risk of developing both mast cell mediated diseases, atopic diseases, and autoimmune diseases excluding thyroiditis and diabetes. CONCLUSION: The autoimmune profile of the comorbidities of CU was demonstrated with an evident risk of developing rheumatoid arthritis. CU patients were also at increased risk of either having or achieving depression. Mast cell related diseases seemed to be overrepresented, although registry data within this disease category are questionable and similar to symptoms of CU to the untrained eye. Thus, CU patients constitute a multimorbid group of patients, which must be recognized among treating physicians.