Association of melasma with thyroid autoimmunity and other thyroidal abnormalities and their relationship to the origin of the melasma.

Melasma is localized hyperpigmentation over the forehead, upper lips, cheeks, and chin. In this study, evidence suggesting an association between autoimmune thyroid disorders and melasma and the relationship of thyroid disorders to the origin of melasma is presented. A total of 108 nonpregnant women, aged 20-56 yr, were divided into 2 groups for the purpose of this study: 1) melasma, 84 patients; 2) control group, 24 patients from the Dermatology Clinic matched for age and sex. Microsomal thyroid autoantibodies (MCHA) were sought in all subjects. TRH-TSH tests were performed in patients with melasma and in those women with goiter and/or positive MCHA tests from the control group. Studies were completed with serum T4, T3, and antithyroglobulin antibody (TGHA) measurements in all patients with thyroid abnormalities. In patients with melasma, the frequency of thyroid disorders (58.3%) was 4 times greater than in the control group. The MCHA-negative patients had 1) simple goiter (13.1%), 2) Plummer's disease (2.4%), and 3) TSH hyperresponse to TRH in nongoitrous patients (10.7%). Patients with positive MCHA tests (32.1%) were divided into 2 subgroups. One comprised those women with an apparently normal thyroid gland and thyroid function (n = 7), while the other included all patients with goiter and/or subclinical hypothyroidism (n = 20). Regarding the origin of the melasma, it was found that 70% of women who developed melasma during pregnancy or while using oral contraceptives had thyroid abnormalities compared to 39.4% of patients with idiopathic melasma. Subjects from the control group had a 12.5% incidence of thyroid abnormalities, and only 8.3% had positive MCHA. Estrogen, progesterone, or both could be the triggering factor in the development of melasma in women who have a particular predisposition toward both melasma and thyroid autoimmunity. Patients with idiopathic melasma had a lower frequency of thyroid abnormalities, suggesting that there may be different genetic patterns linked to autoimmune thyroid disease. We conclude that there is a true association between thyroid autoimmunity and melasma, mostly in women whose melasma develops during pregnancy or after ingestion of oral contraceptive drugs.