Unknown: Pedunculated nodule on the foot
Paulo Morais MD¹, Marcos Guimarães MD², Aurea Canelhas MD², Filomena Azevedo MD¹
Dermatology Online Journal 18 (4): 5

Abstract

Eccrine poroma is a benign adnexal neoplasm composed of epithelial cells with poroid or distal ductal differentiation. We report a healthy 57-year-old woman with a 4-year history of an asymptomatic pedunculated nodule on the lateral border of the right foot that was proven to be an eccrine poroma by histopathologic examination.

Answer: Eccrine poroma

History

An otherwise healthy 57-year-old woman presented with a 4-year history of a pedunculated nodule on the lateral border of the right foot. The growth had slowly enlarged over the years. The patient denied any previous local trauma or significant pain, except when wearing closed shoes. Physical examination revealed a 30 x 28 x 12 mm non-tender, flesh-colored, pedunculated firm nodule with a hyperkeratotic surface that protruded from the border of her right foot (Figure 1).

Figure 1	Figure 2
Figure 1. Clinical appearance of the patient. (A) Lateral view; (B) dorsal view. Note the presence of a well-demarcated erythematous plaque surrounding the lesion that disappeared about a week after excision of the lesion, probably representing a reactive inflammatory process. Figure 2. Histological image (H&E stain) of the tumor showing anastomosing strands of uniform, small, cuboidal, epithelial cells with monomorphous ovoid nuclei, inconspicuous nucleoli, and a moderate amount of pale eosinophilic cytoplasm, without atypia or mitosis (A, magnification x20). These cells were continuous with the basal layer of the epidermis and extended into the upper dermis. Note the presence of small ducts throughout the lesion (B, arrow head, magnification x100), occasional cysts (C, asterisk, magnification x20), and dilated vessels (D, arrow, magnification x100).

The lesion was excised and the specimen was submitted for histopathologic study (Figure 2).

Case presentation

Figure 3
Figure 3. Subtypes of poroma according to Ackerman [1]. The differentiation between subtypes is mainly based on the location of the tumor cells. There are some cases with 2 or more histopathological variants. Therefore, it is sometimes difficult to demarcate sharply among the variants.

The term “poroma” refers to a group of benign adnexal neoplasms with “poroid” or tubular (usually distal ductal) differentiation [1]. The malignant variant of EP, porocarcinoma, is a far less common entity [2]. Like syringoma, poroma has been interpreted historically as a neoplasm of eccrine lineage, mostly because of enzyme histochemical findings of doubtful specificity [3]. Types of poromas include the typical eccrine poroma (EP) as well as its three distinct histological subtypes (Figure 3). These subtypes display varying cellular growth patterns as follows: hidroacanthoma simplex, dermal duct tumor, and poroid hidradenoma [1]. However, more recently it has been suggested that poromas can be a proliferation of either eccrine or apocrine lineage [4]. The difficulty in differentiating both lineages of poromas occurs because the sweat ducts of the two are histologically and immunohistochemically identical. The term acrospiroma is used by some authorities as a synonym for poroma and is used by others as a broad designation that includes both poroma and hidradenoma.

First reported by Pinkus et al in 1956 [5], EPs are believed to comprise 10 percent of all sweat gland tumors, which of themselves represent only 1 percent of all primary cutaneous lesions [6, 7]. The pathogenesis of EP is unknown, although it has been associated with scarring, trauma, and radiation [8, 9]. There is no predilection according to race or sex. It tends to be diagnosed in patients aged from 40-70 years [10]. The most common location is on the foot (47%), although cases have been described on the head, trunk, and upper limbs [1, 7, 8]. Clinical diagnosis of EPs is often difficult because they exhibit a polymorphic gross appearance and may mimic lesions as diverse as pyogenic granulomas, skin tags, warts, cysts, and other adnexal tumors. Although they usually present as skin-colored papules, plaques, or nodules less than 2 cm in diameter, pigmented poromas (from melanin), and erythematous lesions (from dilation or proliferation of blood vessels) have been reported [6, 8]. Surface erosion or ulceration, presumably secondary to trauma, are occasionally reported.

Histologically, EP consists of a circumscribed proliferation of compact cuboidal keratinocytes with small monomorphous nuclei and scant eosinophilic cytoplasm. The degree of ductal differentiation varies greatly in individual neoplasms but is evident in most EPs [6, 8]. Carcinoembryonic antigen (CEA) immuperoxidase staining, which labels the luminal surface of both apocrine and eccrine ducts, can be employed to confirm the presence of ductal differentiation. Poromas can be confined to the epidermis (intraepidermal poroma, or hidroacanthoma simplex), can occur in broad continuity with the epidermis, with extension into the papillary dermis (juxtaepidermal poroma), or can develop wholly (or nearly so) within the dermis (intradermal poroma or dermal duct tumor) [1, 6, 8]. At times, a poroma may display striking clear cell change and may rarely display small foci of necrosis en masse or coagulation necrosis. These features are not of any known clinical significance and, in this case, necrosis en masse is not a clue to a malignancy. In addition, some poromas are accompanied by cystic spaces in the epidermis, hyperkeratosis at the surface of the tumor, or foci of sebaceous differentiation, usually consisting of clusters of mature sebocytes near the lesion base and presumably representing apocrine poromas [11]. Rarely, multiple poromas will develop, either in an acral or in widespread distribution, a clinical pattern referred to as poromatosis [12].

The diagnosis of EP typically cannot be made based exclusively on clinical findings, although experienced clinicians may recognize the entity. The dermoscopic features of pigmented and nonpigmented EPs have recently been described [7, 13]. Pigmented poromas mimic a number of skin tumors, including pigmented basal cell carcinomas, seborrheic keratosis, and malignant melanoma, because they present with various clinical, dermoscopic, and histopathological features [13]. In the case of nonpigmented EP, dermoscopic analysis can help in the differential diagnosis, although neither clinical findings nor dermoscopy can guarantee that we can distinguish such lesions from amelanotic melanoma, porocarcinoma, or squamous cell carcinoma [7]. Therefore, the diagnosis of EP is only fully established after surgical excision with subsequent microscopic examination by a trained dermatopathologist.

The prognosis of EPs is good because the lesions have no known clinical significance. Although it is possible that a significant proportion of eccrine porocarcinomas follows a preexisting EP, which undergoes malignant transformation [1, 14], this risk is minimal and is thought to be similar to that of normal skin.

References

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