Association of oral lichen planus with thyroid disease in a Finnish population: a retrospective case-control study Maria Siponen, DDS, a Lasse Huuskonen, DDS, b Esa Läärä, MSc, c Tuula Salo, DDS, PhD, d Oulu and Kiuruvesi, Finland UNIVERSITY OF OULU AND CITY OF KIURUVESI HEALTH CENTER Objective. The objective of this study was to estimate the association between the history of thyroid disease and the prevalence of oral lichen planus (OLP)/oral lichenoid lesions (OLL). Study design. This was a retrospective case-control study using data from the medical records of 222 OLP/OLL patients and 222 age- and sex-matched controls who had visited the Institute of Dentistry, University of Oulu or the Oral and Maxillofacial Department, Oulu University Hospital, from 1992 to 2001. Clinical characteristics of OLP/OLL lesions, other oral mucosal diseases, presence of cutaneous LP, history of allergies, medical history, and the use of regular medications were recorded. The relative odds of OLP, OLL, and OLP/OLL associated with selected patient characteristics were estimated by logistic regression. Results. History of any thyroid gland pathosis was found in 15% (n = 22) of the 152 cases with OLP, in 13% (n = 9) of the 70 cases with OLL, and in 8% (n = 18) of the control subjects; the estimated odds ratios (with 95% confidence intervals) being 2.12 (1.06 to 4.21) for OLP and 1.57 (0.62 to 3.73) for OLL. When confined to hypothyroidism only, this disease was found in 10% (n = 15) of the OLP cases, 9% (n = 6) of the OLL cases, and 5% (n = 11) of the controls; the estimated odds ratios being 2.39 (1.05 to 5.61) for OLP and 1.73 (0.56 to 4.90) for OLL. Conclusion. The association of OLP/OLL and thyroid disease, especially between hypothyroidism and OLP, calls for further investigations in other populations and into the possible mechanisms behind this association. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;110:319-324) Lichen planus (LP) is an inflammatory mucocutaneous disease that most commonly affects middle-aged fe- males. Reported prevalence of oral lichen planus (OLP) in European adult populations varies from 1% to 3%, being generally higher in women. 1-3 Skin lesions are usually transient, whereas oral mucosal lesions tend to be chronic and rarely undergo spontaneous remission. 3 Erosive forms of OLP may cause considerable discom- fort to the patient. OLP is associated with a slightly elevated risk of malignant transformation. 4 The pathogenesis of OLP probably is mediated by both antigen-specific T-cell mediated and nonspecific immunological mechanisms. 5,6 The initial triggering factor for these immunological events and the subse- quent lesion formation in OLP is still unknown, but viral infection, bacterial products, mechanical trauma, systemic drugs, contact sensitivity, or an unidentified agent have been proposed. 6 Oral lichenoid lesions (OLL) bear clinical and his- topathologic resemblance to OLP, and often cannot be distinguished from OLP. However, in contrast with OLP, the etiological factors for OLL can sometimes be identi- fied, and may include reactions to drugs or dental mate- rials (mainly amalgam) or conditions such as graft-versus- host disease. 7 To gain better understanding of the causes of OLP, systemic associations with it are more actively being sought. Higher frequencies of serum antinuclear (ANA), a Specialist in Oral Pathology, Department of Diagnostics and Oral Medicine, Institute of Dentistry, University of Oulu, Oulu, Finland. b General Dentist, City of Kiuruvesi Health Center, Kiuruvesi, Finland. c Professor, Department of Mathematical Sciences, Faculty of Sci- ence, University of Oulu, Oulu, Finland. d Professor, Department of Diagnostics and Oral Medicine, Institute of Dentistry, University of Oulu, and Oulu University Hospital, Oulu, Finland. Received for publication Sep 18, 2009; returned for revision Mar 27, 2010; accepted for publication Apr 3, 2010. 1079-2104/$ - see front matter © 2010 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2010.04.001 319 Vol. 110 No. 3 September 2010 ORAL MEDICINE Editor: Craig S. Miller