Follicular Lymphomatoid Papulosis: An Eosinophilic-Rich Follicular Subtype Masquerading as Folliculitis Clinically and Histologically.

Lymphomatoid papulosis (LyP) is an uncommon CD30 lymphoproliferative disorder with a relatively excellent prognosis. Ten to twenty percent of cases, however, are associated with a lymphoma, typically systemic or cutaneous anaplastic large cell lymphoma, mycosis fungoides, or Hodgkin lymphoma. Subtypes divide LyP into infiltrate-descriptive categories along a spectrum of histological manifestation. Classically, LyP shows a patchy, wedge-shaped, perivascular dermal infiltrate of small- to intermediate-sized lymphoid cells, larger lymphoid, with one, 2, or multiple prominent nucleoli, and a variable admixture of neutrophils, eosinophils, and histiocytes. Follicular LyP shares these characteristics, although its infiltrate is folliculocentric. Variable folliculotropism, follicular dilation, rupture, and mucinosis can occur. This entity is commonly misdiagnosed and underreporting likely because its histopathologic features can masquerade as more common follicular-based entities. The authors present 2 cases of this rare variant to underscore the importance of clinicopathologic correlation in diagnosis. To the best of the authors' knowledge, this is the first report of the follicular LyP variant with concurrent mycosis fungoides. In the context of a literature review, diagnostic pitfalls and classification of this variant are discussed.