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Linear arrector pili muscle hamartoma on the tail of a sphynx cat 一例斯芬克斯猫尾部线性立毛肌错构瘤 作者：Natalia Fanton, Margherita Orlandi†,and Francesca Abramo 翻译：郭润霞 Arrector pili muscle (APM) hamartoma is reported in humans and dogs. We describe a linear APM hamartoma in a sphynx cat. The lesion was characterized by multiple nodules distributed linearly along the tail, made of randomly arranged hypertrophic smooth muscles, the size of which tended to wax-and-wane during a one year follow-up. 立毛肌(APM)错构瘤在人和犬中均有报道。我们描述了一只斯芬克斯猫的线性APM错构瘤。病变表现为沿尾部呈线性分布的多个结节，由随机排列的肥大平滑肌组成，一年后随访时其大小有消长趋势。
Introduction 介绍 Arrector pili muscle (APM) is a specialized adnexal structure made of smooth muscle fibres. Lesions arising from APMs are rare; piloleiomyoma and piloleiomyosarcoma are the unique examples in cats. Hamartoma of this muscle, with disorganized, mature muscle bundles in their normal anatomical location, is described in humans and more rarely in dogs of different breeds.In humans, congenital and acquired forms have been reported, occurring mainly as solitary lesions in the lumbosacral region.The aim of this case report is to describe the clinical and microscopic features of an APM hamartoma occurring on the tail of a sphynx cat. 立毛肌(APM)是由平滑肌纤维组成的特殊附件结构。起源于APMs的病变罕见；毛发平滑肌瘤和毛发平滑肌肉瘤是猫的特殊情况。立毛肌错构瘤，是在其正常解剖位置有紊乱、成熟的肌束，在人类中有报道，在不同品种的犬中更罕见。在人类中，有先天性和获得性形式的报道，主要发生在腰骶部的独立病变。本病例报告的目的是描述发生在斯芬克斯猫尾部的APM错构瘤的临床特征和显微特征。
Case report 病例报告 A 2-year-old male sphynx cat was presented with several nonpruritic and nonpainful skin nodules on the tail, noticed one month before presentation. General physical examination was unremarkable, with the exception of seven cutaneous nodules arranged in a linear fashion on the dorsal surface of the tail. The nodules were alopecic, 5 mm in diameter and surrounded by skin that was considered to be normal according to the breed type. Some of the nodules were eroded (Figure 1a). Cytological examination of skin surface impression smears revealed neutrophils, eosinophils and rare lymphocytes. Histological examination of the lesions was declined by the owner at the time of initial examination, and because the cat showed no signs of discomfort, no therapy was instituted. 一只2岁的雄性斯芬克斯猫在就诊前一个月发现尾部有几个非瘙痒性和非疼痛性的皮肤结节。除尾部背侧有7个呈线状排列的皮肤结节外，体格检查无异常。结节呈脱毛状，直径5 mm，结节周围有正常皮肤（根据品种认为是正常皮肤）。部分结节表现糜烂（图1a）。皮肤表面压片细胞学检查：中性粒细胞、嗜酸性粒细胞及少见淋巴细胞。初诊时，宠主拒绝对病变进行组织学检查，由于猫未显示不适的症状，因此未进行治疗。
Figure 1. Clinical lesions of linear arrector pili muscle (APM) hamartoma in a sphynx cat. Cutaneous alopecic nodules linearly arranged along the tail (a); two months later, the skin of the tail was hypertrichotic (b). 图1. 斯芬克斯猫线性立毛肌(APM)错构瘤的临床病变。皮肤脱毛结节沿尾部呈线状排列(a)；两个月后尾部皮肤多毛症(b)。
The cat was re-evaluated after two months; the previously observed erosions had resolved spontaneously and two new nodules had arisen. The skin surrounding the nodules showed marked hypertrichosis compared to the rest of the body, and a few hair shafts emerged from the nodules (Figure 1b). Surgical excision of three nodules was performed for histopathological evaluation. Tissue was fixed in 10% neutral formalin and processed routinely; sections were stained with haematoxylin & eosin. All lesions exhibited unencapsulated, expansile, well-demarcated APMs (Figure 2a) which were expanded in number and size, and distributed randomly within the dermis. The APMs did not originate from the follicularisthmus and, rather, closely abutted the follicles. The hypertrophic smooth muscle fibres showed small, tapered, elongated euchromatic nuclei and eosinophilic cytoplasm (Figure 2b). Mitotic activity was very rare. Inflammatory superficial infiltrates were composed of neutrophils, rare eosinophils and lymphocytes. Given the histomorphological findings of hyperplastic APMs which did not maintain their normal spatial relationship to the hair follicles (obliquely connecting the superficial dermis to the isthmus), a diagnosis of APM hamartoma was made. A piloleiomyoma was less likely considering the multinodularity and the lack of interlacing highly cellular bundles of smooth muscle, which characterize this type of neoplasm. 两个月后对猫进行重新评估；先前观察到的糜烂已自行消退，并出现两个新的结节。与身体其余部分相比，结节周围皮肤出现明显的多毛症，结节内出现少数毛干（图1b）。手术切除3个结节进行组织病理学检查。将组织固定在10%中性福尔马林中，并进行常规处理；切片用苏木精和伊红染色。所有病变均显示无包膜、膨胀性、边界清楚的APM（图2a），其数量和大小均扩大，并在真皮内随机分布。APM并非起源于毛囊峡部，而是紧贴毛囊。肥大的平滑肌纤维显示小的、变细的、细长的常染细胞核和嗜酸性细胞质（图2b）。有丝分裂活性非常罕见。浅表炎性浸润由中性粒细胞、罕见的嗜酸性粒细胞和淋巴细胞组成。鉴于增生性APMs的组织形态学表现未保持其与毛囊的正常空间关系（斜向连接真皮浅层与峡部），诊断为APM错构瘤。考虑到平滑肌的多结节和缺乏交错的高细胞束，毛发平滑肌瘤的可能性较小，这是这类肿瘤的特征。
Figure 2. Photomicrographs of an arrector pili muscle (APM) hamartoma in a sphynx cat. (a) Unencapsulated dermal nodule composed of large, randomly orientated APMs. Haematoxylin & eosin, x4. (b) APMs are composed of hypertrophic smooth muscle fibres surrounded by inflammatory cells. H&E 图2：一只斯芬克斯猫立毛肌(APM)错构瘤的显微镜照片。(a)由大的、随机定向的APM组成的无包膜真皮结节。苏木精和伊红染色，4倍.(b)APM由被炎性细胞包围的肥大平滑肌纤维组成。H&E
At the time of recheck two weeks after biopsies were taken, the surgical sites had healed uneventfully and all remaining nodules showed progressive reduction in size and height and partial hair regrowth on the surface (Figure 3a). The surrounding skin was still hypertrichotic. There was a lack of piloerection and vermiform skin response (i.e. pseudo-Darier’s sign) when the skin was stroked. The owner reported that the nodules waxed and waned in size, and at a one year follow-up were still present (Figure 3b). 活检两周后复查时，手术部位已顺利愈合，其余所有结节大小和高度均呈进行性缩小，并且结节表面部分毛发再生（图3a）。周围皮肤仍多毛。当抚摸皮肤时，缺乏竖毛和蚓状皮肤反应（即伪Darier征）。宠主表述结节时大时小，1年后回访时结节仍存在（图3b）。 Figure 3. Clinical follow-up of linear arrector pili muscle (APM) hamartoma of the sphynx cat. Reduction in size and height of lesions, with partial hair regrowth on nodule surfaces two weeks after biopsy (a); at five month follow-up nodules and hypertrichosis were still present (b). 图3. 斯芬克斯猫线性立毛肌(APM)错构瘤的临床回访。活检后两周，病变尺大小和高度减小，部分结节表面毛发再生(a)；5个月回访时，仍存在结节和多毛症(b)。 Discussion 讨论 This case report describes APM hamartoma in a young sphynx cat, with similarities to the same lesion reported in humans and dogs. Although the sphynx is a congenitally alopecic breed, hair follicles are similar to other breeds and APM are described as part of their follicular units.Hamartomas originate from errors in embryological development and may increase in size over time in proportion to the growth of the animal. Although lesion onset occurred at two years of age in this cat, we cannot exclude a congenital origin. 本病例报告描述了一只年轻的斯芬克斯猫的APM错构瘤，与人和犬中报告的相同病变相似。尽管斯芬克斯猫是一种先天性无毛品种，但毛囊与其他品种相似，APM被描述为其毛囊单位的一部分。错构瘤起源于胚胎学发育的错误，随着时间的推移，其大小可能随着动物的生长而成比例地增加。尽管该猫在两岁时表现症状，但我们不能排除先天性起源。
The clinical presentation of the lesions over the dorsum of the tail resembles linear plaques or multiple nodules as have been described in people.The case lacked a pseudo-Darier’s sign; this sign is a distinctive finding for congenital smooth muscle hamartoma in people, yet it is present in only 50% of human cases. Apart from the possible role of inflammation in influencing the size of the nodules, the authors are unable to provide an explanation for the waxing-and-waning of nodule sizes over time. However, biopsy-proven spontaneous regression of hamartomas of different origin has been reported recently. The possibility that surgical excision of three nodules somehow influenced the biological behaviour of the remaining ones cannot be excluded. 如人们所描述的，尾背侧病变的临床表现类似于线状斑块或多发性结节。该病例缺乏伪Darier征；该特征是人类先天性平滑肌错构瘤的特异性症状，但仅存在于50%的人类病例中。除了炎症可能影响结节大小外，作者无法解释结节大小随时间有消长变化。然而，近期有报道证实活检不同来源错构瘤的自发消退。不能排除手术切除3个结节以某种方式影响其余结节的生物学行为的可能性。
Because the lesions caused no functional concerns for the cat and the owner was not interested in complete surgical excision of the remaining nodules, no further intervention was pursued. 由于病变未对猫造成功能性问题，并且宠主对剩余结节的完全手术切除不感兴趣，因此未进行进一步干预。
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发表于 2022-2-10 21:42:23
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