Department of Pathology, The Ohio State University Wexner Medical Center/James Cancer Hospital, Columbus, OH.
Departments of Dermatology and Pathology, Icahn School of Medicine at Mount Sinai, New York, NY.
Am J Dermatopathol. 2024 Jun 1;46(6):377-380. doi: 10.1097/DAD.0000000000002691. Epub 2024 Apr 4.
Cutaneous syncytial myoepithelioma (CSM) is an uncommon and distinct variant of cutaneous myoepithelioma. We aim to present a case of CSM to enhance the recognition of this unique variant, encompassing its clinical characteristics, histopathological features, immunohistochemical staining, and therapeutic approaches.
A 10-year-old girl presented with a dome-shaped nodule located on the skin of her left medial distal arm. Microscopic examination of the skin biopsy revealed a well-defined dermal nodular lesion, surrounded by an epidermal collarette. Tumor cells were composed of epithelioid to spindle-shaped cells with round-to-oval nuclei, small nucleoli, and abundant eosinophilic cytoplasm with a syncytial-like growth pattern. A moderate degree of nuclear pleomorphism was noted. Mitotic activity was not prominent. Immunohistochemical staining revealed positive staining for epithelial membrane antigen, GLUT1, collagen IV, and S100. Smooth muscle actin, CD10, and CD68 showed patchy positivity. CD31, CD34, p63, SOX10, anaplastic lymphoma kinase (ALK), glial fibrillary acidic protein, pankeratin (AE1/AE3/PCK26), Melan-A, and CD1a were negative. Fluorescence in situ hybridization targeting TFE3 and ALK genes was negative. The differential diagnosis included ALK-negative epithelioid cell histiocytoma, epithelioid perineurioma, and CSM. Based on the above findings, a diagnosis of CSM was rendered.
CSM is a benign cutaneous neoplasm composed of sheets of histiocytoid or short spindle cells with pale eosinophilic cytoplasm with a syncytial-like growth pattern. Clinically, CSM often presents as a painless, slow-growing nodule or plaque in a broad anatomical distribution with a preference for the distal extremities. CSM is characteristically positive for epithelial membrane antigen (EMA) and S100 protein and negative for keratins. In challenging cases, molecular testing for EWSR1 gene rearrangement and EWSR1-PBX3 gene fusion aid in confirming the diagnosis.
The histologic features of CSM present a unique set of challenges posing a diagnostic dilemma, as they can bear resemblance to a range of benign and malignant cutaneous neoplasms including ALK-negative epithelioid cell histiocytoma, epithelioid perineurioma, malignant or nevoid melanoma, and epithelioid sarcoma. An accurate diagnosis is crucial for guiding proper clinical management considering that this entity typically demonstrates an excellent prognosis following a complete surgical excision.
皮肤性合胞体肌上皮瘤（CSM）是一种罕见且独特的皮肤肌上皮瘤变体。我们旨在介绍一例 CSM 病例，以提高对这种独特变体的认识，包括其临床特征、组织病理学特征、免疫组织化学染色和治疗方法。
一名 10 岁女孩出现位于左前臂内侧远端皮肤的半球形结节。皮肤活检的显微镜检查显示边界清楚的真皮结节性病变，周围有表皮领状结构。肿瘤细胞由上皮样到梭形细胞组成，具有圆形到卵圆形核、小核仁、丰富的嗜酸性细胞质和类似于合胞体的生长模式。观察到中度核多形性。有丝分裂活性不明显。免疫组织化学染色显示上皮膜抗原、GLUT1、胶原 IV 和 S100 阳性染色。平滑肌肌动蛋白、CD10 和 CD68 呈斑驳阳性。CD31、CD34、p63、SOX10、间变性淋巴瘤激酶（ALK）、神经胶质纤维酸性蛋白、广谱细胞角蛋白（AE1/AE3/PCK26）、Melan-A 和 CD1a 均为阴性。针对 TFE3 和 ALK 基因的荧光原位杂交为阴性。鉴别诊断包括 ALK 阴性上皮样细胞组织细胞瘤、上皮样神经鞘瘤和 CSM。根据上述发现，诊断为 CSM。
CSM 是一种良性皮肤肿瘤，由具有类似合胞体的生长模式的组织细胞样或短梭形细胞组成，具有淡嗜酸性细胞质。临床上，CSM 通常表现为无痛、生长缓慢的结节或斑块，广泛分布于四肢，尤以四肢远端多见。CSM 特征性地表达上皮膜抗原（EMA）和 S100 蛋白，不表达角蛋白。在具有挑战性的病例中，EWSR1 基因重排和 EWSR1-PBX3 基因融合的分子检测有助于确认诊断。
CSM 的组织学特征呈现出一组独特的挑战，构成了诊断难题，因为它们可能类似于一系列良性和恶性皮肤肿瘤，包括 ALK 阴性上皮样细胞组织细胞瘤、上皮样神经鞘瘤、恶性或神经嵴黑色素瘤和上皮样肉瘤。准确的诊断对于指导适当的临床管理至关重要，因为这种实体通常在完全手术切除后具有良好的预后。
