Eccrine Poroma with an Atypical Clinical Presentation Mimicking an Epidermal Nevus

BULLETIN FOR MEDICAL PRACTITIONERS

Dr Swe Swe Win, Visiting Fellow
Dr Chua Sze Hon, Consultant Dermatologist, National Skin Centre

Introduction
Eccrine poroma, a benign tumor originating from eccrine sweat glands, is a fairly common tumor seen at the National Skin Centre. It usually presents as a small solitary lesion of less than 1cm in diameter on the acral regions of the body especially on the soles of the feet. Larger lesions and occurrence on other parts of the body are uncommon clinically and difficult to diagnose without histology. We report a case of eccrine poroma presenting as a verrucous elongated plaque on the thigh of a patient that clinically resembled an epidermal nevus.

Case report
A 53-year-old Chinese female presented to our dermatological clinic with a growth on her left thigh of 20 years duration. The growth was asymptomatic without pain, itch or discomfort but it bothered her as it had been gradually increasing in size over the years. On clinical examination, a pink colored, verrucous plaque measuring 4cm x 1cm was present on the back of the left thigh (Fig.1). The initial clinical diagnosis was that of an epidermal nevus. A skin biopsy was performed and the histology revealed broad anastomosing strands of uniform, small, cuboidal, epithelial cells with lightly basophilic, round nuclei and moderate amount of pale eosinophilic cytoplasm. Intracytoplasmic vacuoles were present within the tumor (Fig. 2). The tumor cells were sharply demarcated from the surrounding normal keratinocytes. Histology confirmed the tumor to be that of an eccrine poroma and the lesion was subsequently completely excised without recurrence.

Discussion
Eccrine poroma is a common tumor of the skin that was first described by Pincus et al in 1956.[1] The tumor originates from benign eccrine sweat glands. It usually occurs as a solitary small lesion on the sole of the foot, hair-bearing regions and hand. Occurrence on other locations are much less common.[2] Cases of head and neck eccrine poromas have been reported and these tumors may have originated from apocrine glands instead of from eccrine glands.[3] Recent reports describing cases with sebaceous, follicular and apocrine differentiation also suggest possible alternative apocrine origin. Benign eccrine poroma have also been reported to occur on the eyelid.[4]

The clinical presentation is typical and the tumor often appears sessile or slightly pedunculated with normal or erythematous color and a firm consistency. Ulceration may occur at points of pressure, but the surface is usually smooth and often lobulated. It may superficially resemble a pyogenic granuloma, hypertrophic scar, hemangioma, dermatofibroma or even a malignant melanoma. Giant forms of eccrine poromas do occur but are extremely rare.[5] Other rare variants include eccrine poromatosis in which multiple (more than 100 papules) occur on the palms and soles or are disseminated throughout the body.[6,7]

Harmatomas with eccrine differentiation are generally quite rare. In a rare variant - acrosyringeal nevus, one may find a linear lesion on a lower extremity[8] or as a solitary verrucous plaque.[9] Histologically, acrosyringeal nevus resembles premalignant fibroepithelial tumor of Pincus, except that the ductal lumen is often present within extended cords and strands of tumor cells. Another rare variant is that of porokeratotic eccrine ostial and dermal duct nevus, which presents as congenital keratotic papules and plaques on the distal extremities.[10]

Histologically, eccrine poroma is composed of broad anastomosing strands of uniform, small, cuboidal, epithelial cells with lightly basophilic, round nuclei and moderate amount of pale to eosinophilic cytoplasm. It frequently demonstrates foci of small tubular differentiation. The tumor needs to be differentiated from clear-cell porocarcinoma--in-situ and eccrine porocarcinoma. Eccrine porocarcinoma is also referred to by some authors as malignant eccrine poroma or malignant hidroacanthoma simplex. Clinically, eccrine porocarcinomas present as verrucous plaques or polypoid growths which often bleed with minor trauma.[11] The diagnosis can be prefaced by an in-situ stage. The malignant form of eccrine poroma is exceedingly uncommon compared to the benign form and originates from the intraepidermal ductal portion of the eccrine gland. Incidence is less than 0.01 % of all skin biopsy specimens.[12] There is a 50% metastasis rate to regional lymph nodes and overall prognosis is often poor.[12,13] In total contrast, benign eccrine poroma has an excellent prognosis after complete surgical excision. Incomplete removal, however, may lead to local recurrence. If malignancy is suspected, wide excision & long-term follow-ups are essential.

References

1. Pincus H et al. Eccrine poroma: tumors exhibiting feature of epidermal sweat duct unit. Arch Dermatol 1956; 74:511.
2. Okun MR, AnseIl HB. Eccrine poroma - report of two cases with an unusual location. Arch Dermatol 1963; 88:56 1-566.
3. Moore TO, Orman HL, Orman SK, Helm KF. Poromas of the head and neck. J Am Acad Dermatol 2001; 44(1):48-52.
4. Vu PP, Whitehead KJ, Sullivan TJ. Eccrine poroma of the eyelid. Clin Exp Ophthalmol 2001; 29(4):253-5.
5. Carvajal Balaguera J J et al. Giant eccrine poroma. Mapere Medicina 1995; 6:136-138.
6. Goldner R: Eccrine poromatosis. Arch Dermatol 1970;10 1:606.
7. Wilkinson RD et al. Hidrotic ectodermal dysplasia with diffuse eccrine poromatosis. Arch Dermatol 1977; 113:472.
8. Ogino A. Linear eccrine poroma. Arch Dermatol 1976;112:841.
9. Weedon 0, Lewis J. Acrosyringeal Nevus. J Cutan Pathol 1997; 4:166.
10. Sassmannshausen J et al. Porokeratotic eccrine ostial and dermal duct nevus: a case report and review of the literature. JAm Acad Dermatol 2000; 43:364-7.
11. Ghislain PD, Marot L, Tennstedt 0, Lachapelle JM. Eccrine porocarcinoma with extensive cutaneous metastasis. Ann Dermatol Venereol 2002; 129(2):225-8.
12. Maeda T, Mon H, Matsuo T et al. Malignant eccrine poroma with multiple visceral metastasis: report of case with autopsy finding. J Cutan Pathol 1996; 53:566-70.
13. Kacker A, Shaha AR. Ductal eccrine carcinoma arising in the postaural area. Ear Nose Throat J 1999; 78:576-7.

DEDICATED TO EXCELLENCE IN DERMATOLOGY
By National Skin Centre (Singapore)
Copyright (C) 1995 - National Skin Centre (Singapore)
 

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