Possible link between Hashimoto's thyroiditis and oral lichen planus: a novel association found

Hashimoto's thyroiditis as well as lichen planus has been associated to a number of disorders, generally of auto-immune origin. A novel possible association between oral lichen planus (OLP) and Hashimoto's thyroiditis (HT) is here proposed on the basis of a cross-sectional survey.

One hundred and five unrelated OLP patients were considered. Diagnosis of HT was based on positive serum anti-TPO, anti-Tg, TSH levels and the typical ultrasound pattern of the thyroid gland.

In the present survey, the prevalence of HT in the OLP group was 14.3 % whereas the prevalence of HT-related hypothyroidism in the general population was reported to be equal to 1 %. By Fisher's exact test, it was revealed that the difference between our data and historical prevalence of HT was found statistically significant.

Actually, there is no definitive hypothesis that could explain the coexistence of OLP and HT. However, considering the onset timing of HT followed by OLP in 93.3 % of our series, we suspected a causal or predisposing role for HT. Specifically, we believe that in HT patients, circulating thyroid antibodies could contribute to trigger an organ-specific auto-immune response also in the oral mucosa or skin, leading to the development of LP lesions.

Because of the large number of cases of asymptomatic chronic auto-immune thyroiditis, it would be useful that women over 40 years of age affected by OLP were screened for thyroid dysfunction, particularly HT.