Pityriasis Lichenoides-like Mycosis Fungoides: Clinical and Histologic Features and Response to Phototherapy

BACKGROUND: Pityriasis lichenoides (PL)-like skin lesions rarely appear as a specific manifestation of mycosis fungoides (MF). OBJECTIVE: We investigated the clinicopathological features, immunophenotypes, and treatments of PL-like MF. METHODS: This study included 15 patients with PL-like lesions selected from a population of 316 patients diagnosed with MF at one institution. RESULTS: The patients were between 4 and 59 years of age. Four patients were older than 20 years of age. All of the patients had early-stage MF. In all patients, the atypical lymphocytic infiltrate had a perivascular distribution with epidermotropism. The CD4/CD8 ratio was <1 in 12 patients. Thirteen patients were treated with either narrowband ultraviolet B (NBUVB) or psoralen+ultraviolet A (PUVA), and all of them had complete responses. CONCLUSION: PL-like MF appears to have a favorable prognosis and occurrence of this variant in adults is uncommon. MF should be suspected in the case of a PL-like skin eruption. Therefore, biopsy is required to confirm the diagnosis of PL-like MF, and NBUVB is a clinically effective treatment.