The Diagnosis: Poroma
Histopathology showed an endophytic expansion of the epidermis by bland, uniform, basaloid epithelial cells with focal ductal differentiation and an abrupt transition with surrounding epidermal keratinocytes (Figure), consistent with a diagnosis of poroma. The patient elected to monitor the lesion rather than to have it excised.
Poroma. A, Histopathology revealed broad columns of basaloid cells with focal ductal differentiation connected to the epidermis extending into the dermis, along with areas of hyalinized stroma and blood vessels (H&E, original magnification ×40). B, A sharp transition of poroma cells with the adjacent epidermal keratinocytes was noted (H&E, original magnification ×100).
Eccrine poroma, used interchangeably with the term poroma, is a rare benign adnexal tumor of the eccrine sweat glands resulting from proliferation of the acrosyringium.1,2 It often occurs on the palms or soles, though it also can arise anywhere sweat glands are present.1 Eccrine poromas often appear in middle-aged individuals as singular, well-circumscribed, red-brown papules or nodules.3 A characteristic feature is a shallow, cup-shaped depression within the larger papule or nodule.1
Because the condition is benign and often asymptomatic, it can be safely monitored for progression.1 However, if the lesion is symptomatic or located in a sensitive area, complete excision is curative.4 Eccrine poromas can recur, making close monitoring following excision important.5 The development of bleeding, itching, or pain in a previously asymptomatic lesion may indicate possible malignant transformation, which occurs in only 18% of cases.6
The differential diagnosis includes basal cell carcinoma, circumscribed acral hypokeratosis, Kaposi sarcoma, and pyogenic granuloma. Basal cell carcinoma is the most common type of skin cancer.7 In rare cases it has been shown to present on the palms or soles as a slowgrowing, reddish-pink papule or plaque with central ulceration. It typically is asymptomatic. Histopathology shows dermal nests of basaloid cells with peripheral palisading, stromal mucin, and peritumoral clefts. Treatment is surgical excision.7
Circumscribed acral hypokeratosis presents on the palms or soles as a solitary, shallow, well-defined lesion with a flat base and raised border.8 It often is red-pink in color and most frequently occurs in middle-aged women. Although the cause of the condition is unknown, it is thought to be the result of trauma or human papillomavirus infection.8 Biopsy results characteristically show hypokeratosis demarcated by a sharp and frayed cutoff from uninvolved acral skin with discrete hypogranulosis, dilated blood vessels in the papillary dermis, and slightly thickened collagen fibers in the reticular dermis.9 Surgical excision is a potential treatment option, as topical corticosteroids, retinoids, and calcipotriene have not been shown to be effective; spontaneous resolution has been reported.8
Kaposi sarcoma is a vascular neoplasm that is associated with human herpesvirus 8 infection.10 It typically presents on mucocutaneous sites and the lower extremities. Palmar involvement has been reported in rare cases, occurring as a solitary, well-demarcated, violaceous macule or patch that may be painful.10-12 Characteristic histopathologic features include a proliferation in the dermis of slitlike vascular spaces and spindle cell proliferation.13 Treatment options include cryosurgery; pulsed dye laser; and topical, intralesional, or systemic chemotherapy agents, depending on the stage of the patient’s disease. Antiretroviral therapy is indicated for patients with Kaposi sarcoma secondary to AIDS.14
Pyogenic granuloma presents as a solitary red-brown or bluish-black papule or nodule that bleeds easily when manipulated.15 It commonly occurs following trauma, typically on the fingers, feet, and lips.6 Although benign, potential complications include ulceration and blood loss. Pyogenic granulomas can be treated via curettage and cautery, excision, cryosurgery, or pulsed dye laser.15