Clinical and histologic differentiation between lymphomatoid papulosis and pityriasis lichenoides.

The relationship between lymphomatoid papulosis and pityriasis lichenoides is a matter of considerable debate. Differentiation between these two conditions is, however, important because patients with lymphomatoid papulosis, unlike those with pityriasis lichenoides, may develop systemic lymphoma and thus require long-term follow-up. In our study the clinical and histologic features of eighty-two patients with pityriasis lichenoides and twenty-six patients with lymphomatoid papulosis were reviewed and compared. Clinical and histologic differences were recognized, not only allowing differentiation between the two conditions, but also suggesting that they are pathogenetically distinct diseases. Finally, evidence is presented to suggest that the different views on the relationship between these diseases mainly result from differences in patient selection.