Pigmented eccrine poroma in an unusual site: Dermoscopy and histopathology correlation in skin of color

Dear Sir,

Eccrine poroma is an uncommon benign adnexal tumor due to terminal ductal differentiation. Goldman et al. described it for the 1^st time in the literature.^[1] The major differences between eccrine poroma and ductal poroma are epidermal location and connection to epidermis in the former, while the latter is located in the deep dermis and not connected to epidermis. While eccrine poromas (EP) are commonly found on acral regions, Pigmented EP (PEP) is typically observed on non-acral sites, particularly in individuals with darker skin tones.^[1,2]

Clinically, EPs are variable, appearing as pink-to-red papules, plaques, or nodules. However, establishing a definitive diagnosis of EP, especially its pigmented variant, is challenging based solely on clinical and dermoscopic findings. PEP can clinically simulate cutaneous melanoma or basal cell carcinoma (BCC), earning EP the title of “the great dermoscopic imitator” due to its resemblance to various benign and malignant skin neoplasms. Despite the utility of non-invasive tools such as dermoscopy in narrowing the differential diagnosis, histopathological examination remains fundamental for definitive diagnosis.^[3,4]

We present a 35-year-old man who came with a solitary, asymptomatic lesion on the forehead for a month. Examination revealed a well-circumscribed, raised, pigmented nodule measuring 1.5 × 1.5 cm. No history of associated pain or pruritus. Borders were sharply demarcated. Irregular, tiny nodulations with erosion and pigmented specs were noted on the surface [Figure 1a]. The nodule was soft in consistency.

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Figure 1:

(a) Clinical image of pigmented eccrine poroma showing a circumscribed nodule with erosions and pigmented specs on the surface. (b) Dermoscopy shows irregular black clods (yellow arrows), comedo-like openings (white arrow), and white areas (black arrows). Yellowish-grey rim (white stars) surrounding black clods and white areas, and dotted and glomerular vessels (yellow box) are well appreciated (Hand-held DermLite 4, ×10 magnification, polarised mode).

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Dermoscopic evaluation was done by hand-held DermLite 4 with ×10 magnification in polarised mode, which revealed marked asymmetry in both morphological structure and pigmentation. Black clods of irregular size and shape, and white structureless areas with dotted and glomerular vessels were noted. A yellowish-gray rim was seen surrounding both these structures. Comedo-like openings are found. Surface scales were noted in a few areas [Figure 1b].

Histopathology demonstrated broad anastomosing tumor strands connected to the flattened epidermis at a few places [Figure 2a]. Within the tumor cells, variably sized melanin granules were identified [Figure 2b]. Neoplastic proliferation composed of uniform poroid (cuboidal) cells with evidence of poroid differentiation showing maturation into well-formed small ductal lumina [Figure 3a]. Dilated capillaries were noted within the tumor strands [Figure 3b].

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Figure 2:

(a) Histopathology shows anastomosing tumor strands attached to epidermis (star) (hematoxylin and eosin [H and E], ×10). (b) Histopathology shows cellular constituents of the tumor admixed with melanin (arrow) (H and E, ×40).

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Figure 3:

(a) Histopathology shows smaller and darker poroid cells and pinkish cuticular cells with a moderate amount of melanin (yellow arrow) (hematoxylin and eosin [H and E], ×40). (b) Histopathology shows dilated capillaries (black arrow) amongst tumor cells (H and E, ×10).

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Based on the correlation of the histopathological findings with the clinical and dermoscopic features, a final diagnosis of pigmented eccrine poroma was established.

PEP is a benign adnexal tumor that typically presents as a firm, flesh-colored to erythematous nodule, papule, or plaque, generally located in non-acral sites. Clinically, pigmented eccrine poroma can mimic a range of other lesions, including seborrheic keratosis, epithelialized pyogenic granuloma, BCC, angiofibroma, and cutaneous melanoma, often making accurate diagnosis challenging.^[3]

The dermoscopic features of eccrine poroma have been only partially characterized in the literature. In a series of non-pigmented lesions, the most consistent findings included a white-to-pink halo surrounding the vessels, pink-white structureless areas, and a variety of vascular patterns such as glomerular, linear, irregular, and hairpin vessels.^[3,5] In contrast, the pigmented variant was distinguished by prominent vascular structures along with globule-like areas and comedo-like openings as its principal dermoscopic hallmarks.^[2]

In the present case, the clinical lesion was well-circumscribed with erosions on the surface mimicking angiofibroma and seborrheic keratosis. Dermoscopy demonstrated white areas with vessels and irregular black clods and a yellowish-gray rim. Dermoscopy and histopathological correlation; white areas are due to squamous differentiation, dotted and glomerular vessels correspond to capillary dilatation, black globules and comedo-like openings are pigmented tumor mass exposed to the surface. Yellowish-gray rim correlates with a network of tumor strands within the dermis in approximation to the epidermis.

To conclude, PEP is a rare adnexal tumor that can closely mimic both benign and malignant pigmented lesions, leading to potential diagnostic pitfalls. This case emphasizes the importance of correlating clinical, dermoscopic, and histopathological findings to achieve an accurate diagnosis and avoid unnecessary aggressive treatment. Complete surgical excision remains curative, with an excellent prognosis.