Eccrine poroma on the face: an atypical presentation.

An eccrine poroma is a solitary tumor arising from the eccrine duct epithelium in the epidermis. The lesions commonly occur on the sole of the foot, the hands, and occasionally on the nose, eyelids, neck, and chest. We report a patient who presented with a slow-growing nodular lesion over her left cheek, prompting a diagnosis of basal cell carcinoma or keratoacanthoma. Biopsy from the nodule revealed a well-defined epidermal tumor with uniform small cuboidal cells with rounded deeply basophilic nuclei, few narrow ductal lumina, and occasional cystic spaces confirming the diagnosis of an eccrine poroma.

What was known?

Eccrine poroma is a benign neoplasm of the eccrine gland commonly seen over the palms and soles. Lesions on atypical sites present a diagnostic challenge and histopathologic features are the key to confirmation of the diagnosis.

Introduction

Eccrine poroma is a benign neoplasm of the acrosyringium. Poromas usually occur on the palms and soles.[12] We report a patient with a slow-growing ulcerated nodule over the face clinically simulating a basal cell carcinoma; however, unexpectedly, the biopsy revealed the growth to be an eccrine poroma. The tumor, often consisting of broad anastomosing bands of uniform appearing cuboidal cells arising within the epidermis and extending downward into the dermis.[23] There is a sharp line of demarcation between the adjacent epidermis and the tumor cells. Occasionally, poromas may be of divergent adnexal differentiation in which case, immunohistochemistry studies may have to be performed.[4]

Case Report

A fifty-year-old woman presented with a slow-growing nodule over the left cheek for one and a half years. The lesion started as a tiny, 2 mm asymptomatic papule on the left cheek and gradually increased to 2 cm in size. There was no history of trauma, pre-existing skin lesion, or topical application at the site of the lesion. There was no family history of similar lesions.

Examination revealed an ulcerated nodule with a peripheral hyperpigmented rim just lateral to the left nasolabial fold [Figure 1]. The lesion was about 1.5 cm in diameter, firm, mobile, non-tender, and did not bleed on touch. The local lymph nodes were not enlarged. Differential diagnoses considered were basal cell carcinoma, squamous cell carcinoma, amelanotic melanoma, and keratoacanthoma.

Figure 1

Ulcerated nodule with peripheral hyperpigmented rim over left cheek

Excision biopsy was performed, which surprisingly revealed broad anastomosing bands of uniform small cuboidal cells [Figure 2], few ductal lumina, and narrow cystic spaces [Figure 3] within the epidermis. Further, the cuboidal cells showed uneven cytoplasmic clearing [Figure 4]. The histological features clinched the diagnosis of an eccrine poroma. A few occasional mitoses were seen which suggested the requirement of a close follow-up in this patient.

Figure 2

Broad anastomosing bands of uniform small cuboidal cells

Figure 3

Few ductal lumina and narrow cystic spaces within the epidermis

Figure 4

Cuboidal cells showing uneven cytoplasmic clearing

Discussion

Eccrine poroma was first described by Goldman et al. in 1956.[5] The term ‘poroma’ refers to a group of benign adnexal neoplasms with ‘poroid’ or terminal ductal differentiation.[2] Clinically, poromas usually present as solitary papules, plaques, or nodules usually over the palms and soles but may appear on any cutaneous surface where they tend to mimic benign and malignant melanocytic and non-melanocytic lesions. About two-third of cases are seen on soles or sides of soles followed by hands and fingers, and rarely over the face.[67] Most of the lesions appear in middle-aged or elderly individuals.[8]

Eccrine poroma may exhibit polymorphic features that can make the diagnosis difficult. Differential diagnosis of eccrine poromas described in previous case reports includes pyogenic granuloma, hemangioma, seborrheic keratosis, verruca, fibroma, melanoma, nevus, cysts, and basal and squamous cell carcinoma.[67]

Eccrine poroma arises within the lower portion of the epidermis and extends downward into the dermis. The tumor cells are uniformly cuboidal with a round basophilic nucleus, and are connected by intercellular bridges. The border between the tumor and the stroma is well defined. The tumor cells contain significant amount of glycogen which is associated with cytoplasmic clearing. Most eccrine poromas show ductal lumina and occasional cystic spaces within the tumor bands which are lined by an eosinophilic, periodic acid-schiff PAS-positive, diastase-resistant cuticle.[12]

Eccrine poromas may be situated entirely within the epidermis where the tumor cells form discrete aggregates. These intraepidermal poromas are described as ‘hidroacanthoma simplex’. When eccrine poromas are located within the dermis, they consist of tumor islands of various shapes with ductal lumina; these are described as ‘dermal duct tumors’.[2]

Enzyme histochemical staining shows prevalence of eccrine enzymes such as phosphorylase and succinate dehydrogenase.[1]

Some benign neoplastic proliferations with histopathologic features of “eccrine” poroma could be of apocrine origin. Immunohistochemistry studies reveal that poroid cells are exclusively positive for Cytokeratin (CK) 1/5/10/14, CK5/8, and CK14, which are expressed in the outer cells of normal dermal sweat ducts and stain heterogeneously with anti-CK7, CK8/18, CK10/11, and CK19 antibodies which react in the inner cells of dermal ducts and in the secretory cells of sweat glands. Based on the keratin immunohistochemistry, the neoplastic cells in eccrine and apocrine poromas are considered to be closely related to the cells of dermal sweat ducts and it is difficult to differentiate apocrine poroma from eccrine poroma by keratin expression patterns alone.[4]

Genetic studies reveal p53 protein expression in eccrine poroma.[9]

Poromas, being benign adnexal neoplasms; treatment is optional. Electrosurgical destruction, carbon dioxide laser-assisted removal, or surgical excision may be performed. Topical treatments such as 1% atropine solution have been reported to be beneficial in treatment of superficial lesions.[210]

Conclusion

Forman[3] et al., in their article on eccrine poroma, describe it as a tumor with many faces. The asymptomatic nodule on our patient's face which was masquerading as a cutaneous carcinoma clinically proved to be an eccrine poroma histopathologically.

Even though an eccrine poroma has typical histopathological features, it has a propensity toward varied clinical presentations. Hence, such atypical nodules require a biopsy for confirmation of diagnosis and further management. Enzyme immunohistochemistry and genetic studies help in typifying poromas better.[11]

What is new?

Eccrine poroma on the face is a rare occurrence. It may simulate many benign and malignant skin tumors. A biopsy is the key for management of these patients.