Association between oral lichen planus and Hashimoto thyroiditis: A systematic review

Background Oral Lichen Planus (OLP) and Hashimoto Thyroiditis (HT) are autoimmune, chronic and inflammatory diseases sharing common pathogenetic mechanisms, involving T lymphocytes and chemokines, predominantly affecting middle age women. Only few metanalyses have generically investigated the correlation between OLP and autoimmune diseases or thyroid disorders. This Systematic Review aimed to investigate the association between OLP and HT. Methods MEDLINE, Cochrane Central Register of Trials, EMBASE, Google Scholar and Web of Science, up to December 1 st 2022, were searched. Clinical trials and observational studies were considered. Risk of bias assessment was performed using the JBI’s Critical Appraisal Tool. The association between OLP and HT was estimated by the Mantel–Haenszel odds ratio (MH-OR); a subgroup metanalysis was performed considering different diagnostic criteria of HT. Results From 6288 titles identified, 33 papers were evaluated for eligibility and 5 studies were included. A higher risk of HT in OLP patients (MH-OR=2.29, [95% C.I. 1.43, 3.67]; p=0.006), compared to non-OLP individuals, was found. Heterogeneity among included studies was low (. The overall risk of bias was high. When HT diagnosis was performed through evaluation of both thyroid autoantibodies’ titers and thyroid function tests, the association was strengthened (MH-OR= 2.35 [95% C.I. 1.47, 3.75]; p=0.004), with low heterogeneity (I 2 =0%) and unclear risk of bias. Conclusions OLP patients may be at increased risk of HT. Clinicians should consider HT as a frequent OLP comorbidity and carry out adequate diagnostic tests in suspected cases of HT. The cooperation between stomatologists and endocrinologists, to ensure adequate care for patients affected by both diseases, should be recommended. Further studies are needed to better investigate the possible cause-and-effect relationship between OLP and HT.