Dermatology

Poroma (Eccrine Poroma, Hidroacanthoma Simplex, Dermal Duct Tumor)

Poroma (Eccrine Poroma, Hidroacanthoma Simplex, Dermal Duct Tumor)

Are You Confident of the Diagnosis?

Characteristic findings on physical examination

Poromas usually present as asymptomatic solitary lesions in the middle-aged or elderly. These lesions are typically located on palmar or plantar skin, but may occur in any area where eccrine glands are present. Clinically, a poroma is described as a sharply demarcated 2-12 mm papule or nodule, usually flesh or pink in color, though a pigmented variant has been reported (Figure 1).

Figure 1.

Poroma on medial foot.

While poromas are commonly asymptomatic, it is important to inquire about a history of pain, bleeding, or pruritus as these qualities are more common with porocarcinomas.

The clinical differential diagnosis is comprised of both benign and malignant neoplasms including pyogenic granuloma, melanocytic nevus, seborrheic keratosis, angioma, dermatofibroma, clear cell acanthoma, neurofibroma, soft fibroma, amelanotic melanoma, squamous cell carcinoma, basal cell carcinoma, Merkel cell carcinoma, and porocarcinoma.

Expected results of diagnostic studies

Dermoscopic examination of a poroma reveals much variability including a white-to-pink halo around the vessels, glomerular vessels, linear irregular vessels, hairpin vessels, and/or multiple pink-white structureless areas. Unfortunately, since these findings are commonly seen in amelanotic melanoma, nonmelanoma skin cancer, and porocarcinoma, dermoscopic examination is of little diagnostic value for poromas.

Therefore, histopathologic examination is required for definitive diagnosis of poroma. Histopathology of poroma reveals a circumscribed tumor of uniform basaloid or poroid cells extending from the epidermis into the upper dermis with few pale larger cells and small ducts and/or cysts scattered within (Figure 2, Figure 3). The stroma is typically comprised of telangiectatic vessels.

Figure 2.

Hematoxylin and eosin stain of poroma (×20).

Figure 3.

Another example of hematoxylin and eosin stain of poroma (×20).

Diagnosis confirmation

Confirmation of a poroma diagnosis is dependent on histopathologic exam as described above. Variations in the histology have been reported.

Poromas with sebaceous differentiation have been described, showing scattered sebocytes among the poroid cells. This raises the question of apocrine differentiation in this subtype. While eccrine and apocrine glands have distinct functions, they both arise from downgrowths of the epidermis around the fourth month of gestation and therefore do have some common cellular precursors.

Hidroacanthoma simplex has been described as a purely intraepidermal poroma, while a dermal duct tumor has been described as an intradermal poroma. We have included hidroacanthoma simplex and dermal duct tumor as synonymous with poroma since most authors consider these tumors similar both clinically and histologically with the same derivation simply found at different locations within the skin. In addition, studies have shown that serial sections of dermal duct tumors do reveal a connection to the epidermis.

Who is at Risk for Developing this Disease?

Poromas most commonly present in the middle-aged and elderly population with a reported average age of 68 years. Most studies do not show a difference in the incidence of poromas between genders or among races. There have been isolated case reports of poromas presenting in association with sites of trauma, chronic radiation dermatitis, or burn injury.

What is the Cause of the Disease?

Etiology

While there have been few associations with various types of trauma, the exact cause of poroma development is unknown.

Pathophysiology

Many immunohistochemical studies have been performed to determine the cellular derivation of poromas. Since the poroid cells of the tumor express cytokeratin 14 (CK14) and do not express cytokeratin 1 (CK1), cytokeratin 6 (CK6), cytokeratin 7 (CK7), cytokeratin 10 (CK10), CD34, or cytokeratin 77 (CK77); it is concluded that these arise from the basal keratinocytes of the eccrine duct ridge and lower acrosyringium. The scattered larger cells within the tumor do express CK1 and CK10 suggesting a ductal differentiation.

Systemic Implications and Complications

Poromas typically present as solitary lesions and have no known systemic implications. Rare case reports have described multiple poromas, or poromatosis, but no systemic disorder has been definitively associated with this rare condition. There has been one case reported of poromatosis in a patient with hidrotic ectodermal dysplasia, but a clear association has not been determined.

Treatment Options

Treatment options for poroma are summarized in Table I.

Table I.

Treatment options for poroma
Medical treatment Surgical Procedures Physical Modalities
Imiquimod 5% cream Surgical excision Clinically monitor

Optimal Therapeutic Approach for this Disease

Since many malignant tumors are in the clinical differential of a poroma, biopsy and histopathologic examination is necessary for diagnosis. Unfortunately, if the biopsy is too superficial and the entire lesion including the base cannot be visualized. or there are secondary changes, there may still be a concern for the presence of malignant degeneration of porocarcinoma within the residual lesion. It has been reported that 18-50% of porocarcinomas appeared to have arisen in continuity with a preexisting benign poroma.

Considering the above, if a representative biopsy is performed and a diagnosis of poroma is determined, clinical monitoring for recurrence or malignant degeneration is the management approach of choice. If there is limited sampling of the biopsy specimen, or if the patient complains of symptoms such as bleeding, pain, or pruritus, there may be a concern for porocarcinoma. In this case, surgical excision in the treatment of choice. In making the decision on the management of a benign neoplasm by surgical excision, the location of the lesion, especially if acral, and the morbidity associated with such an excision should be taken into account.

There is a single case report in the current literature which reports successful treatment with topical 5% imiquimod cream (3 times each week for 4 weeks) of a solitary poroma on the face of a patient who refused surgery. Further studies with appropriate follow-up are necessary before using this therapeutic option as first-line treatment.

Patient Management

A patient with a history of a poroma should be monitored for recurrence or malignant degeneration of the lesion as well as development of additional poromas. If a lesion becomes symptomatic or changes suddenly, a surgical excision should be performed due to the concern for malignant degeneration. The incidence of malignant degeneration is difficult to assess, but studies quote 18-50% of porocarcinomas arise from benign poromas.

Unusual Clinical Scenarios to Consider in Patient Management

There have been isolated case reports of poromatosis, including one associated with hidrotic ectodermal dysplasia. Depending on the number of lesions present, excision of the many poromas in poromatosis may be impractical. Close clinical monitoring of these lesions is recommended.

What is the Evidence?

Ackerman, AB, Abendoza, P. "Neoplasms with eccrine differentiation". Lea & Febiger. 1990. pp. 113-85.

(A well-referenced chapter of the first complete histopathologic description of poroid neoplasms.)

Battistella, M, Langbein, L, Peltre, B, Cribier, B. "From hidroacanthoma simplex to poroid hidradenoma: clinicopathologic and immunohistochemical study of poroid neoplasms and reappraisal of their histiogenesis". Am J Dermatopathol. vol. 32. 2010. pp. 459-68.

(A thorough retrospective clinicopathologic review of poroid neoplasms and their immunohistochemical analysis with cytokeratin 10 (K10), K14, K77, and Ki67.)

Chen, CC, Chang, YT, Liu, HN. "Clinical and histological characteristics of poroid neoplasms: a study of 25 cases in Taiwan". Int J Derm. vol. 45. 2006. pp. 722-7.

(A clinicopathologic analysis of 25 poroid neoplasms, mostly poromas.)

Ferrari, A, Buccini, P, Silipo, V. "Eccrine poroma: a clinical-dermoscopic study of seven cases". Acta Derm Venereol. vol. 89. 2009. pp. 160-4.

(A clinical and dermoscopic analysis of seven poromas.)

Jo, JH, Chin, HW, Kim, MB. "A case of eccrine poroma treated with 5% imiquimod cream". J Dermatol. vol. 32. 2005. pp. 691-693.

(A single case report of a patient who refused surgical excision of a facial poroma treated with 5% imiquimod 3 times each week for 4 weeks. Pre- and posttreatment histologic evaluation was performed.)

Kurashige, Y, Yamamoto, T, Okubo, Y, Tsuboi, R. "Poroma with sebaceous differentiation: report of three cases". Austral J Derm. vol. 51. 2010. pp. 31-4.

(A case series of three poromas with sebaceous differentiation.)

Lallas, A, Chellini, PR, Guimaraes, MG. "Eccrine poroma: the great dermoscopic imitator". J Eur Acad Dermatol Venereol. 2015.

(A brief description of the variability of dermoscopic findings of poromas with clinical and dermoscopic images.)

Langbein, L, Cribier, B, Schirmacher, P. "New concepts on the histiogenesis of eccrine neoplasia from keratin expression in the normal eccrine gland, syringoma and poroma". Br J Derm. vol. 159. 2008. pp. 633-45.

(An immunohistochemical study of normal eccrine glands, syringoma, and poroma using antibodies to keratins, smooth muscle actin, and Ki67.)

Missall, TA, Burkemper, NM, Jensen, SL, Hurley, MY. "Immunohistochemical differentiation of four benign eccrine tumors". J Cutan Pathol. vol. 6. 2009. pp. 190-6.

(An immunohistochemical study of normal eccrine glands, cylindroma, poroma, spiradenoma, and syringoma using antibodies to cytokeratin (CK) 6, CK7, CK10, CD10, CD34, and smooth muscle actin.)

Sawaya, JL, Khachemoune, A. "Poroma: a review of eccrine, apocrine, and malignant forms". Int J Dermatol. vol. 52. 2014. pp. 1053-61.

(A review of the clinical presentations, histopathologic findings, and treatment options of poroid tumors as well as the differential diagnoses.)

Sidro-Sarto, M, Guimera-Martin-Neda, F, Perez-Robayna, N. "Eccrine poroma arising in chronic radiation dermatitis". JEADV. vol. 22. 2008. pp. 517-19.

(A single case report of poroma arising in chronic radiation dermatitis and a brief review of similar literature.)

Wilkinson, RD, Schopflocher, P, Rozenfeld, M. "Hidrotic ectodermal dysplasia with poromatosis". Arch Dermatol. vol. 113. 1977. pp. 472-6.

(A single case report of poromatosis in association with hidrotic ectodermal dysplasia.)

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