An inflamed trichilemmal (pilar) cyst: Not so simple?

Abstract

Context: Trichilemmal (pilar) cysts are common skin lesions that often present on the scalps of mature men and women. These cysts often become inflamed when the wall of the cyst ruptures, but few reports have addressed the immunologic features of this process.

Case report: A 22-year-old female presented with rapidly growing nodule on her left cheek, with evidence of acute inflammation. Skin tissue for hematoxylin and eosin examination, as well as for immunohistochemical analysis was taken and reviewed. As controls, we utilized two archival, non-inflamed trichilemmal cysts. Hematoxylin and eosin staining demonstrated classic features of an inflamed trichilemmal cyst. No cytologic atypia was noted, and no significant number of mitotic figures was identified. Immunohistochemistry stains revealed that several cell cycle/tumor suppressor/apoptotic markers, antigen presenting cell markers, metalloproteinases and T cell response markers were highly expressed inside and around the disrupted cyst. The control, non-inflamed cysts were negative for the same markers. CD1a was also appreciated within the epidermis, suprajacent to the inflamed cyst.

Conclusions: Upregulation and/or downregulation of selected cell cycle regulator and/or tumor suppressor/apoptotic markers, as well as antigen presenting cells and some protein kinases could recruit and activate T lymphocytes and other inflammatory cells to the non-disrupted cyst for unknown reasons. The immune response may be involved in the initial cyst rupture, or induced by an unknown alteration in the cyst. Larger studies are needed to address these questions.

Keywords: BCL-10; Trichilemmal (pilar) cyst; cytokeratin A1/A3; matrix metalloproteinase-9 (MMP9); p27kip1; vimentin.

Fig. 1

a. H & E staining shows the series of cyst in the epidermis at 40x magnification. b similar but at 100x, and in this case one of the cyst is broken (blue arrow). c. Similar but in this case the lower part of the cyst is observed (blue arrow). d. IHC staining using Cytokeratin AE1/AE3 antibody shows the positive staining inside the cyst (brown stain) (blue arrow). e. Same antibody as d, but the stain is not only in the cyst but also in some of the “apparently normal pilosebaceous units” around the cyst (red arrows). f. and g similar that e, at higher magnification. Please note that some of the areas around the cyst are also positive with the Cytokeratin AE1/AE3 antibody (red arrow). h and i, IHC using vimentin. Please note some compartamentalization of this antibody around the cyst (red arrow).

Fig. 2

a Positive staining with the antibody to Cytokeratin A1/A3 antibody around the wall of the cyst and inside in (red arrow). b through e positive staining with p27 antibody in the wall of the cyst as well as in some spots inside the cyst (red arrows). f. IHC using MMP9 showing some positive staining in the wall of the cyst as well as inside it (red arrows). g. MMP9 (positive in some cells of the sebaceous glands (red arrows) (dark staining). h, MMP9 stain showing how some parts of the cyst are being separated from the adjacent matrix and staining positive for MMP9 on both sites of the gap (red arrow) (dark brown stain). i. Positive staining in some spots inside the cyst using TIMP1 antibody (dark staining, red arrows).

Fig. 3

a. Zap-70 positive staining in some spots inside the cyst (dark staining; red arrows). b. Positive staining in some spots inside the cyst using TIMP1 antibody (dark staining; red arrows). c, d, and e. p27 positive staining in areas of pilosebaceous units that are apparently “normal” by histology (brown staining; red arrows). p27 stains around other partially damaged cysts, and inside the sebaceous glands (red arrows). f. Positive staining inside the cyst in some patches with alpha 1 anti-trypsin (red arrow). g. BAX positive staining in a patch inside the cyst, and also in the inflammatory infiltrate outside the cyst (dark staining; red arrows). h. BAX positive staining in the inflammatory infiltrate around the cyst (red arrow). i. BCL-10 positive staining in the inflammatory infiltrate around the cyst (red arrow).