Lymphomatoid papulosis followed by pityriasis lichenoides: a common pathogenesis?

Pityriasis lichenoides (PL) and lymphomatoid papulosis (LyP) are uncommon idiopathic eruptions with overlapping clinical and histological features. Although current opinion indicates that PL and LyP are distinct and separate entities, molecular genetic evidence of T-cell clonality in both conditions suggests that an etiopathogenic relationship may exist. We report a patient who was diagnosed with LyP type B in 1985 followed by PL after 11 years. We hypothesize that LyP followed by PL in the same patient reflects differences in the host immune response to a common antigenic stimulus.