Thyroid autoimmunity in chronic urticaria

Chronic urticaria (CU) is an autoimmune process in some patients. An association between CU and autoimmune thyroid disease has also previously been proposed. Our group has identified functionally significant histamine-releasing autoantibodies in one subset of CU patients (subset 1), predicted by positive autologous intradermal serum tests and positive histamine release from donor basophil leucocytes in vitro. Sera from a second subset of patients (subset 2), all of whom had positive autologous intradermal serum tests, failed to release histamine from donor basophils. A final disease subset (subset 3) has no identifiable skin reactivity (negative autologous serum skin test) or in vitro histamine releasing activity.

In order to examine further the possible relationships between thyroid autoimmunity, thyroid dysfunction and CU, we have examined thyroid autoantibodies and thyroid-stimulating hormone (TSH) levels (an indirect measure of thyroid dysfunction) in the three CU subsets.

We studied 182 patients (69% female), of whom 90 had a positive autologous intradermal serum test.

Eighteen skin test-positive and four skin test-negative patients had thyroid microsomal antibodies (TMA). TSH outside the normal range was found in 13 skin test-positive and one skin test-negative patient. These findings represent clustering of TMA positivity [risk ratio (RR) 4.06, 95% confidence interval (CI) 1.56-10.6] and of abnormal thyroid function (RR 15.5, CI 2.07-11.6) among the skin test-positive patients. However, in the overall study group an elevated TSH was present in seven patients (3.8%, CI 1.6-7.8) comparable to the 5% expected prevalence in the community. Thyroglobulin antibodies (TGA) were present in two of 182 patients.

There were significant differences between skin test-positive and skin test-negative patients with regard to autoimmune thyroid disease. Evidence for autoimmune thyroid disease and abnormal thyroid function was largely found among the skin test-positive patients, supporting the theory of an autoimmune aetiology in this group.