Plaque-type syringoma is uncommon, and its presentation as discrete flat plaques on the scalp is even rarer [1]. Other types of syringoma that are relatively more common include eruptive, local, familial, and syndrome-associated types [5]. Majority of syringomas affect females particularly the face [3]. To the best of our knowledge, this is the first report of plaque-type syringoma presenting as flat, dusky, discrete plaques on the scalp and the ear. Histopathology results for PTS usually show a tumor arising from eccrine coils, forming cysts and coma-shaped duct with extensive fibrosis surrounding the lesion [4]. Notably, only 14 other cases have been reported with plaques on the face, neck, trunk, penis, and acral areas [6].
Although the pathophysiology of syringoma remains largely unknown, it has been suggested that chronic inflammation is a possible mechanism driving its development [7]. Genetic studies have also revealed autosomal dominant inheritance patterns in some families. One of the chromosomes is shown a type of Chromosome 16q22 [8]. Certain syndromes, such as Down’s, Ehler Danlos, Nicolau–Balus, and Marfan, have been associated with syringomas [6]. Notably, syringomas associated with Nicolau–Balus syndrome are mostly widespread lesions, while those associated with Down syndrome are either localized or widespread [3]. The female predominance of syringomas can be explained by hormonal factors. This has been confirmed by the increased occurrence of syringomas before and around puberty [7].
The differential diagnoses of PTS include microcystic adnexal carcinoma (MAC), morphea from basal cell carcinoma (BCC), and desmoplastic trichoepithelioma (DTE) [1]. Malignant tumors such as sweat gland carcinoma and metastatic adenocarcinoma should also be considered in the differential diagnosis and excluded through appropriate diagnostic testing. It is paramount to differentiate MAC from PTS because of the multiple cases of patients subjected to unnecessary surgical procedures due to misdiagnosis. Therefore, clinicians should be aware of these two diseases [9]. To confirm the diagnosis, a conservative elliptical excision with subsequent longitudinal sectioning should be performed to examine the biopsy specimen in its entirety. The overall architecture should be evaluated, including the depth and nature of involvement (whether continuous or discontinuous). In MAC, asymmetric single-cell-line ductal structures show perineural invasion. PTS is usually limited to the upper dermis; however, MAC infiltrates the dermis, hypodermis, bone, muscle, and cartilage [2]. Moreover, MAC is rapidly growing, whereas PTS has an indolent course [9]. In this patient’s case, the tumor was discontinuous and involved only the dermis, supporting a diagnosis of benign ductal proliferation and saving the patient from unnecessary surgical procedures [1].
Unlike most PTS cases, our patient’s tumor extended deep into the reticular dermis. According to the literature, only one prior case of PTS has been reported to involve the deep reticular dermis and penile shaft [4]. Histological morphology can also help rule out morphea from basal cell carcinoma and DTE, which lack ductal differentiation, unlike PTS. Morpheaform BCC is histologically characterized by nuclear atypia and mitotic figures, whereas DTE often has cytokeratin-20 positive Merkel cells [9]. The patient’s histopathological results were negative for features suggestive of morpheaform BCC or DTE. Other diagnostic modalities, such as immunohistochemistry and electron microscopy, can be used to further characterize lesions [6].
Treatment options for plaque-type syringoma include surgical excision, cryotherapy, CO2 laser ablation, or electrocautery [10]. Of these, CO2 laser is considered the most effective treatment option, although it does not provide complete resolution [1]. Rarely, regression of syringomas is observed in adults [7].
Given the benign nature of the lesion, observation and monitoring may be a reasonable management strategy in many cases. Treatment decisions should be individualized based on patient symptoms, lesion characteristics, and cosmetic concerns. Unnecessary surgical procedures should be avoided unless there is strong histopathology findings supporting its need.
The strength of this case report stems from its thoroughness in terms of establishing the accurate diagnosis as supported by histopathology and immunohistochemistry findings. Its weakness however, may be attributed to the fact that patient has not been followed up for a prolonged period of time to ascertain that there is no regression of the lesion. Regardless, the patient was given a return date for six months after establishing diagnosis at which point the lesion will be reassessed for any features suspicious for malignancy.