Dermatopathic lymphadenopathy (DL) is a distinctive type of lymph node hyperplasia that typically occurs in the setting of chronic dermatologic diseases. DL generally self-resolves following disappearance of the underlying skin stimulus and does not require any specific therapy. We recently observed multiple myeloma oncogene 1/interferon regulatory factor 4 (MUM1/IRF4) expression in a case of DL using immunohistochemical methods. The goal of this study was to systematically assess DL cases for MUM1/IRF4 expression and to survey other histiocytic and Langerhans cell lesions. We particularly focused on Langerhans cell histiocytosis (LCH) because the differential diagnosis of DL versus LCH in lymph nodes can be challenging. We identified high expression of MUM1/IRF4 in all 22 cases of DL tested. Specifically, MUM1/IRF4+ dendritic cells comprised 50% to 90% (median, 80%) of all dendritic cells in the paracortex of dermatopathic lymph nodes, always showing moderate or strong intensity. Among 10 DL cases stained for MUM1/IRF4 and langerin/CD207 using dual immunohistochemistry, MUM1/IRF4+ and langerin+ Langerhans cells represented 5% to 60% (median, 30%) of paracortical dendritic cells. MUM1/IRF4 was also positive in reactive Langerhans cells in skin biopsy specimens of all cases of spongiotic dermatitis (n=10) and normal skin (n=15), and was negative in all cases of LCH (n=24), Rosai-Dorfman disease (n=10), follicular dendritic cell sarcoma (n=5) and histiocytic sarcoma (n=4). In aggregate, our findings support the utility of MUM1/IRF4 to highlight the dendritic cells of DL and to distinguish DL from other histiocytic and Langerhans cells lesions.

皮肤病性淋巴结病 (DL) 是一种独特类型的淋巴结增生，通常发生在慢性皮肤病的情况下。DL 通常在底层皮肤刺激消失后自行消退，不需要任何特殊治疗。我们最近使用免疫组织化学方法观察了 DL 病例中多发性骨髓瘤癌基因 1/干扰素调节因子 4 (MUM1/IRF4) 的表达。本研究的目的是系统评估 DL 病例的 MUM1/IRF4 表达并调查其他组织细胞和朗格汉斯细胞病变。我们特别关注朗格汉斯细胞组织细胞增多症 (LCH)，因为淋巴结中 DL 与 LCH 的鉴别诊断可能具有挑战性。我们在所有 22 例 DL 测试病例中均发现 MUM1/IRF4 高表达。具体来说，MUM1/IRF4+树突状细胞占皮肤病淋巴结副皮质中所有树突状细胞的 50% 至 90%（中位数为 80%） ，始终呈现中等或强强度。在使用双重免疫组织化学对 10 例 DL 病例进行 MUM1/IRF4 和 langerin/CD207 染色时，MUM1/IRF4+ 和 langerin+ Langerhans 细胞占副皮质树突状细胞的 5% 至 60%（中位数为 30%）。在所有海绵状皮炎病例 (n=10) 和正常皮肤 (n=15) 的皮肤活检标本中，MUM1/IRF4 在反应性朗格汉斯细胞中也呈阳性，而在所有 LCH 病例 (n=24) 中呈阴性，Rosai-多夫曼病 (n=10)、滤泡树突细胞肉瘤 (n=5) 和组织细胞肉瘤 (n=4)。总的来说，我们的研究结果支持 MUM1/IRF4 突出树突状细胞的效用DL 并将 DL 与其他组织细胞和朗格汉斯细胞病变区分开来。