A double-blind study of twenty-eight patients with severe oral lichen planus treated with etretinate (75 mg daily) or a placebo for 2 months, showed that the oral retinoid had a marked beneficial effect. Nine non-responders who had received only placebo then entered an open cross-over study and they responded well to etretinate. Etretinate thus provided effective symptomatic relief for severe oral lichen planus, but side-effects were common, and six patients stopped treatment because of them.

Several types of human papilloma viruses (HPV) have been associated with benign and malignant squamous cell tumours of mucosal epithelium. To identify HPV in erosive oral lichen planus (OLPe), considered as a premalignant lesion, tissues from 20 patients were examined by Southern blot hybridization with 32P-labeled HPV DNA probes. Type 11 was found in 6 of the lesions while HPV types 6, 16 and 18 were not detected in any of the tissues examined. Using a type-specific polymerase chain reaction (PCR) assay for HPV-6, 11, 16 and 18, HPV-11 was detected in 8 of the samples (all of those positive by Southern blot), and, in addition, HPV-6 was found in 5 samples and HPV-16 in 3 samples. Overall, by the more sensitive PCR assay, 65% of samples were positive for HPV DNA. The finding of HPV DNA in many of the samples using two different techniques indicates a high prevalence of HPV in the OLPe afflicted oral mucosa. However, the role of HPV in the pathogenesis of OLPe has yet to be determined.

67 patients with oral lichen planus of the atrophic-erosive or reticular plaque type were examined. Dental amalgam in contact with mucosal lesions was present in 64 patients, and gold fillings in 33. Patch testing with a standard procedure was performed with components of dental fillings. 11 patients (16%) reacted to at least one of the mercury compounds compared to 8% in a reference group. Most positive reactions were caused by elemental mercury and ammoniated mercury. No patient reacted to gold or copper. Readings at days 10-14 did not increase the number of responders. 13 patients were patch tested with palladium; all were negative. It is not clear whether in the mercury-positive patients allergy to dental amalgam is a causative or aggravating factor, or merely on epiphenomenon.

In order to demonstrate Langerhans' cells in epithelium of oral lichen planus, monoclonal antibodies were used as immunological markers in combination with immunohistochemistry. By the use of anti‐Ia antibodies the Langerhans' cells were shown to express an increased number of Ia‐like antigens in comparison to the amounts found in healthy oral mucosa. The subepithelial infiltrate of mononuclear cells expressed identical Ia‐like antigens on their surfaces. With anti‐T6 antibodies as immunological markers, the number of Langerhans' cells was found to be virtually identical in diseased and healthy epithelium. Treatment of oral lichen planus with tretinoin resulted in a decrease of epithelial Ia‐like antigens compared with the number found in untreated lesions. However, treatment with tretinoin did not alter the frequency of Langerhans' cell marked with anti‐T6 antibodies. The present data demonstrate an increased amount of la‐like antigens per number of T6‐positive Langerhans' cells in diseased oral mucosa compared to healthy conditions. The increased expression of Ia‐like antigens on Langerhans' cells and the contemporary finding of Ia‐like antigens on the subepithelial T‐cells support the opinion that the pathogenesis of oral lichen planus is mainly a cell‐mediated type of immunological reaction.

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