The significance of eosinophils in hypertrophic lichen planus

Background Hypertrophic lichen planus (LP) is a variant of LP favoring the lower extremities and showing prominent epidermal hyperplasia and hyperorthokeratosis. Contrary to dogma that eosinophils are rare in LP and variants, we noticed that some cases of hypertrophic LP have eosinophils in the absence of drug history. Methods Retrospective review of all cases of hypertrophic LP over 22 consecutive years was conducted. The number of eosinophils in 10 representative x20-fields was counted in the area of densest dermal infiltrate. Cases of classic LP were used for comparison. Clinical parameters on all cases were recorded. Results The two groups were clinically similar. The average number of eosinophils per 10 x20-fields in 63 cases of hypertrophic LP was 10.5 with a range between 0 and 200. Thirteen of 63 cases (20.6%) had more than 10 eosinophils per 10 x20-fields. The average number of eosinophils in 17 cases of classic LP was 1.6 (p = 0.016) with a range between 0 and 9 and no cases with more than 10 eosinophils (p = 0.06). Conclusion Hypertrophic LP is a distinct variant of LP that may show variable numbers of eosinophils and should be included in the differential diagnosis of lichenoid dermatitis with eosinophils.