Pityriasis Lichenoides, Atypical Pityriasis Lichenoides, and Related Conditions

Pityriasis lichenoides (PLs) is an uncommon skin disease of unknown etiology. In recent years, an atypical form of PL has been described, showing overlapping features with mycosis fungoides (MF) and lymphomatoid papulosis. We studied 66 patients with an initial histopathologic diagnosis of PL (M:F=34:32; median age, 25 y; range, 7 to 85 y). According to clinical and phenotypic features, cases were classified into 4 categories: (1) Conventional PL (characteristic clinical features of PL without phenotypic aberrations) (n=20; M:F=8:12; median age, 37 y; range, 9 to 74 y); (2) Atypical form of PL (characteristic clinical features of PL with phenotypic aberrations) (n=25; M:F=16:9; median age, 21 y; range, 7 to 72 y). Four of these patients subsequently developed MF; (3) Lymphomatoid papulosis (waxing and waning lesions and positivity for CD30) (n=10; M:F=4:6; median age, 41 y; range, 16 to 83 y); (4) MF (clinical features typical of MF) (n=11; M:F=6:5; median age, 17 y; range, 8 to 85 y). Molecular analyses of clonality of the infiltrate did not reveal relevant differences among these 4 groups. Our study suggests that patients with an initial histopathologic diagnosis of PL may belong to different groups, showing that clinicopathologic correlation and complete phenotypic analyses are paramount in order to achieve proper classification. Although the relationship between PL and MF is yet a matter of debate, at the present state of knowledge, patients with a clinicopathologic presentation consistent with PL but with aberrant phenotypic features should be monitored in order to detect a possible evolution into MF.