Pseudolymphomatous Folliculitis

Abstract

We report the clinical, histopathologic, and immunohistologic features of 15 cases of pseudolymphomatous folliculitis (PLF). The patients comprised seven males and eight females (mean age, 38.6 years; age range, 2-67 years). All patients had dome-shaped or flat-elevated nodules suggestive of cutaneous lymphoid hyperplasias (CLHs). The lesions were solitary in all 15 cases, except in one case with duplex lesions. All lesions were located on the face and measured less than 1.5 cm. In 14 cases with one lesion each, five lesions showed rapid regression after incisional biopsy, whereas the remaining nine underwent excisional biopsy. In the case with duplex lesions, one regressed spontaneously after excisional biopsy of the other. Histopathologically, all PLFs showed dense lymphocytic infiltrates from the dermis to the subcutis simulating cutaneous lymphomas. The walls of hair follicles in all cases were enlarged and irregularly deformed with their epithelium blurred by lymphocytic infiltrates; we called this change "activation" of hair follicles. In nine cases, many atypical lymphocytes were intermingled; three of these cases had been misdiagnosed as cutaneous T-cell lymphoma at other institutions. Immunohistologically, 10 and 5 cases showed predominantly B cells and predominantly T cells, respectively. Remarkably, all lesions showed increased numbers of perifollicular histiocytes expressing anti-S-100 protein and CD1a, and seven lesions showed histiocytes in aggregates. We conclude that PLF is a subset of CLH with characteristic clinical and pathologic features showing perifollicular clustering of T-cell-associated dendritic cells with activation of pilosebaceous units. PLF is an entity to be differentiated from malignant lymphomas and other cutaneous pseudolymphomas.

Multiple nodules on the left cheek represented pseudolymphomatous folliculitis

“…Thereafter, only approximately 10 reports on PLF, including 76 cases, have been published; thus, it is considered to be a rare entity. According to those past reports, typical PLF is presented as a solitary, erythematous or violaceous, dome‐shaped or flat elevated nodule on the face, especially on the nose, cheek, eyelid, or forehead 4, 5. In many cases, the eruption is isolated 5, whereas our patient showed a relatively rare pattern of eruption, as the PLF manifested as multiple lesions.…”

“…Thus, careful histological and immunohistochemical examinations are needed for accurate diagnosis of PLF 1. Arai et al 4 proposed histological criteria for diagnosis, including nodular dense lymphocytic infiltration from the dermis to subcutis, befitting the term pseudolymphoma, in which lymphocytes surround and infiltrate the pilosebaceous unit, and deform the walls. Kazakov et al 5 presented 42 cases of PLF in which hair follicles were enlarged and often distorted, with a dense diffuse lymphoid infiltration composed mainly of small well‐differentiated lymphocytes, occupying the whole dermis, though sparing of the epidermis was also observed.…”

“…Kazakov et al 5 presented 42 cases of PLF in which hair follicles were enlarged and often distorted, with a dense diffuse lymphoid infiltration composed mainly of small well‐differentiated lymphocytes, occupying the whole dermis, though sparing of the epidermis was also observed. Immunohistologically, PLF can be divided into four groups: predominance of B cells, predominance of B cells with fairly numerous T cells, predominance of T cells with fairly numerous B cells, and predominance of T cells 4. Recently, Goyal et al 2 reported that PD‐1+ T cells and CD1a are useful for differentiation of PLF.…”

Solitary Small- to Medium-Sized Pleomorphic T-Cell Nodules of Undetermined Significance: Clinical, Histopathological, Immunohistochemical and Molecular Analysis of 26 Cases

“…To date, only a few, small, heterogeneous series of cases of SMPTCL have been published [3,4,5,6,7,8]; thus, clinical features, prognosis and optimal treatment modalities are not well characterized. In this context, it should be underlined that precise diagnostic criteria for the differentiation of SMPTCL from benign lesions (pseudolymphomas) are lacking, and cases with clinicopathological features overlapping with those of SMPTCL have been reported under different names, including ‘solitary lymphomatous papule, nodule or tumour’ [13], ‘cutaneous lymphoid hyperplasia’ [14], ‘solitary non-epidermotropic T-cell pseudolymphoma’ [15], ‘pseudolymphomatous folliculitis’ [16, 17] and ‘unilesional mycosis fungoides’ [18]. Cases reported recently as ‘indolent CD8+ lymphoid proliferation of the ear’ [19] or ‘pleomorphic CD8+ small/medium size cutaneous T-cell lymphoma’ [20] may represent a phenotypic variant of the same pathological process, too.…”

Pseudolymphomatous Folliculitis on the Nose

“…As atypical lymphocytes can be observed in PLF, it must be differentiated from primary malignant cutaneous lymphomas, including small/medium-sized pleomorphic T cell lymphoma and follicle center B-cell lymphoma, and pilotropic mycosis fungoides [3, 4, 5, 6]. However, in contrast to lymphomas, lymphocytes in PLF show no bias in their κ-/λ-chain-positive B cell ratio or CD4+/CD8+ T cell ratio.…”