RESUMEN
Type of study: prevalence study. Objectives: despite pityriasis lichenoides is an uncommon dermatosis, we observed 12 cases in the last 3 years. By this means, we review clinical and histopathologic findings of all patients with pityriasis lichenoides seen at our Division. Furthermore, since pathogenic features of the disease are unknown, we performed HLA class I and II typing to search for possible immunogenetic markers for pityriasis lichenoides. Methods: twenty-one patients with biopsy-proven diagnosis of pityriasis lichenoides were evaluated. HLA class I and II antigens were typed using conventional serological procedures. Results: children and young adults were predominantly affected. Most of the cases were seen in fall and winter time. Typical disseminated lesions were observed more frequently. Both acute overrepresented in patients (P < 0.005). Conclusions: although pityriasis lichenoides remains a cutaneous disease of undetermined origin, our findings show that the disease is associated with the HLA-B17 antigen