A section is shown at high magnification in Figure 1. What is the clue and what is the diagnosis?
What is the clue and what is the diagnosis?
Plasmacytoid (hyaline) cells are a clue of myoepithelioma.
The photomicrograph shown in Figure 1 comes from a biopsy taken from the nose of a 12-year-old girl (Fig. 2A). A myxoid neoplasm with smooth margins is located in the deep dermis, alcian blue stain is positive in the myxoid stroma (Figs. 2B-C). The cells are arranged as single cells or small trabecules within a prominent myxoid stroma (Figs. 2D-E). At high power, the neoplastic cells have a hyaline cytoplasm and look like plasma cells (Fig. 2F). Immunohistochemically, the cells are positive for AE1/AE3 (Fig. 2G), CAM5.2, vimentin, S100 (Fig. 2H), but negative for desmin, smooth muscle actin, muscle specific actin, CEA, and EMA.
Clinical aspect of the lesion: A smooth nodule on the nose.
A myxoid neoplasm with smooth margins in the deep dermis.
Alcian blue stain is positive in the myxoid stroma.
The cells are arranged in single cells or small trabecules.
The cells are arranged in single cells or small trabecules, some cells show plasmacytoid appearance.
Plasmacytoid cells in a myxoid background.
The cells are positive for AE1/AE3.
The cells were positive for S100.
Myoepithelial cells are located at the periphery of the secretary portion of a glandular organ. They originate embryologically from the ectoderm but show bidirectional differentiation displaying both epithelial and mesenchymal features on morphological, immunohistochemical, and ultrastructural grounds. Neoplasms with myoepithelial differentiation such as myoepithelioma and mixed tumor are well-established entities of salivary glands.  Both of them can show myoepithelial differentiation and are thought of as a continuum. Myoepithelioma was defined as neoplasm with no glandular differentiation or only microscopic foci of glandular differentiation. Cutaneous myoepithelioma was firstly reported in 1998 and a rare cutaneous myoepithelial carcinoma has also been reported. [2-4] Cutaneous myoepithelioma is defined as a neoplasm located mostly in the dermis, sometimes the subcutaneous tissue could be involved but it was not the major part.  Cutaneous myoepithelioma always presented as papule or nodule on extremities and the head and neck region. Histopathologically, it was a well circumscribed, but an unencapsulated nodule in the dermis without connection to the overlying epidermis. The patterns of growth can be solid, myxoid, or reticular. Focal adipocytic metaplasia is present in some cases. Myoepithelial cells always show spindled, epithelioid, and plasmocytoid appearances. The plasmacytoid cells containing pale eosinophilic cytoplasm and ovoid or round nuclei without prominent nucleoli are also named hyaline cells and they are a characteristic sign of myoepithelioma.
Immunohistochemically, the cells usually have a variable expression of vimentin, keratins, epithelial membrane antigen (EMA), S-100 protein, muscle actin, glial fibrillary acidic protein, and calponin. [2-6] The histopathological and immunohistochemical characteristics of this case suggested the diagnosis of cutaneous myoepithelioma. The differential diagnosis of cutaneous mucinous carcinoma was excluded because the neoplasm had a benign silhouette and it lacked fibrous septa. Myxoid glomous tumor was excluded after immunohistochemistry. The case presented here demonstrates the clinical location of a cutaneous apocrine mixed tumor, suggesting that cutaneous myoepithelioma and cutaneous mixed tumor are closely related clinical entities.
A clue to the diagnosis of a myoepithelioma is presented as a quiz. Myoepitheliomas are neoplasms composed of myoepithelial cells, which always show spindled, epithelioid, and plasmocytoid appearances. The plasmacytoid cells containing pale eosinophilic cytoplasm and ovoid or round nuclei without prominent nucleoli are also named hyaline cells and they are a clue to myoepithelioma. We present a case of a myxoid myoepithelioma located on the nose of a 12-year-old girl. Histopathologically, it was composed of single cells and small trabecules in a myxoid stroma. The plasmacytoid cells suggested the diagnosis of myoepithelioma, which was confirmed by immunohistochemical staining. Because of its clinical features, this case also shows that cutaneous myoepithelioma and cutaneous mixed tumor are closely related entities.
Dr. Lei Wang is a dermatologist and Dr Tianwen Gao is Professor and Director of Department of Dermatology, Xijing Hospital in Xian, China. This article was reviewed by Almut Böer, M.D. Contact corresponding author via e-mail: email@example.com .
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