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Pseudolymphomatous Folliculitis with Marked Lymphocytic Folliculo- and Focal Epidermotropism— Expanding the Morphologic Spectrum

Petersson, Fredrik MD, PhD

American Journal of Dermatopathology: May 2011 - Volume 33 - Issue 3 - pp 323-325
doi: 10.1097/DAD.0b013e3181d8e375
Letter to the Editor

Department of Pathology, National University Health System, Singapore

To the Editor:

The term pseudolymphomatous folliculitis (PLF), first coined by Kibbi et al1 denotes a cutaneous lymphoid infiltrate mostly occurring in the facial region with characteristic hyperplastic and distorted hair follicles and, to a lesser extent, hyperplasia of sweat glands with a peculiar “blastoid” transformation of the luminal epithelium. In 1999, Arai et al2 published a series of 15 cases on this topic followed by additional 7 cases in 2005.3 The largest study to date on PLF is by Kazakov et al4 comprising 42 cases which were characterized in great detail including comprehensive both immunohistochemical and molecular genetic studies. In this study, 17 of the 42 cases showed lymphocytic folliculotropism which was “always discrete and focal” and none of the cases showed involvement of the epidermis. Recently, I was confronted with an excisional biopsy of a solitary, 1.5 cm dome-shaped lesion on the left cheek of 4 weeks duration from a previously healthy 55-year-old woman. On examination, the lesion was a lymphoid infiltrate with clinical, histomorphological, and immunohistochemical features conforming to PLF. On routine histology, there was an intense dermal lymphoid infiltration, focally extending into the subcutis, with several enlarged, distorted, and focally disrupted hair follicles. In the periphery of the lesion, several hair follicles were present which displayed marked lymphocytic folliculotropism. The lymphocytes in the follicular epithelium were small with no atypical or cerebriform nuclear features and they did not form aggregates/Pautrier-type abscesses (Fig. 1). There was no evidence of follicular mucinosis. Focally, in the epidermis overlying a few of the involved hair follicles, there was moderate lymphocytic epidermotropism. Also in these areas were the lymphocytes devoid of atypical features and did not form Pautrier abscesses. In addition, several enlarged eccrine units were present with enlarged epithelial cells showing “blastoid” nuclear morphology. No lymphocytic syringotropism was noted. Immunohistochemically, the infiltrate was predominantly composed of (CD3+, CD5+, CD7+) T lymphocytes with a 7:3 ratio in relation to (CD20+, CD10−) B lymphocytes. The T lymphocytes were composed of equal numbers of CD4+ and CD8+ cells. The lymphocytes both within the follicular epithelium and epidermis were almost exclusively T cells (Fig. 2). The bulk of the dermal lymphocytic infiltrate was composed of small lymphocytes with scattered larger (blastoid) cells with moderately large nucleoli. Some plasma cells were identified but no lymphoid follicles were present and CD21 did not show any follicular dendritic cell meshwork. In addition, and as described by Arai et al, small collections of CD68-positive histiocytes were present, notably around the irregularly hyperplastic hair follicles. Moreover, and also characteristic for PLF, a heavy colonization of the follicle epithelium and the perifollicular connective tissue by numerous dendritic cells which were positive for S100 protein and CD1a were present (Fig. 2). CD30 positivity was seen in only a few of the larger “activated” blastoid cells. There was no immunereactivity for CD56.

I am not aware of any cases in previous published reports on pseudolymphomatous folliculitis2-11 with the degree of folliculotropism and the presence of epidermotropism as seen in this case. I did not perform any molecular genetic analysis to investigate whether monoclonality could be discerned, firstly because the clinical, histological, and immunohistochemical findings were typical of PLF and secondly, based on the follow-up data presented by Kazakov et al, the finding of monoclonality does not seem to convey any relevant prognostic or predictive information in PLF and does not change the treatment. However, as suggested by Kazakov et al, it should be noted that PLF may be perceived as a pattern of skin adnexal transformation that may occur, albeit infrequently, in bona fide skin lymphomas. The patient is recently diagnosed and is followed closely.

Fredrik Petersson MD, PhD

Department of Pathology, National University Health System, Singapore

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