A periungual eccrine poroma masquerading as amelanotic melanoma: a case report

Introduction

Eccrine poroma (EP) is a benign cutaneous tumor originating from the acrosyringium of eccrine sweat glands (1). Palms and soles are the most commonly affected area as the eccrine glands are abundant in these places (2,3). However, they can also arise on other areas of the body, such as the head, neck, trunk, and external genitalia (4). They usually present as solitary, asymptomatic, well-circumscribed, smooth or verrucous papules or nodules that range in color from skin-colored to red or brown. The diagnosis of EP is often based on clinical suspicion and confirmed by histopathology. However, some cases may be difficult to diagnose clinically, especially when the distribution and morphology are not typical. Herein, we report a rare case of a periungual EP which reminds us to pay special attention to differential diagnosis of periungual lesions. We present this article in accordance with the CARE reporting checklist (available at https://cco.amegroups.com/article/view/10.21037/cco-24-94/rc).

Case presentation

A 52-year-old man presented to Huashan Hospital, Fudan University with a 2-year history of a painless, slowly growing, erythematous nodule on the lateral nail fold of his right toe. He had no history of trauma, nail-biting, manicure, or chemical exposure. The patient denied any personal or family history of skin cancer or atypical moles. On physical examination, a 2 cm × 2 cm red nodule with a rough surface and well-defined margins was noted on the lateral nail fold of the right toe (Figure 1). The nodule was non-tender and bled easily. The nail plate appeared yellow and dystrophic. Full body skin examination was unremarkable.

Figure 1 Eccrine poroma on the right toe. (A) An erythematous nodule around the nail unit. (B) Clinical manifestations after toenail plate removal.

The differential diagnosis included pyogenic granuloma, keratoacanthoma, basal cell carcinoma, squamous cell carcinoma, and amelanotic melanoma. The clinical suspicion for amelanotic melanoma was high. After removing the nail plate, a biopsy was performed under local anesthesia and the specimen was sent for histopathological examination. Histopathological revealed a tumor composed of broad anastomosing bands of cuboidal cells with eosinophilic cytoplasm and round nuclei within the dermis (Figure 2). The tumor cells were arranged in solid nests or duct-like structures containing luminal eosinophilic material. There was no evidence of atypia, mitosis, necrosis, or invasion. Immunohistochemical staining showed positivity for cytokeratin AE1/AE3 and negativity for S100 protein and HMB-45. The diagnosis of EP was established based on the histopathological and immunohistochemical findings.

Figure 2 Histopathological of eccrine poroma. (A) Neoplasm consisting of small cuboidal cells with ample cytoplasm. The neoplasm is connected to the epidermis but there is no peripheral palisading (hematoxylin & eosin staining, ×20). (B) Uniform small cuboidal cells with round nuclei and moderate amount of cytoplasm (hematoxylin & eosin staining, ×100).

The patient was informed of the diagnosis and underwent complete surgical excision of the lesion with 1 mm margins. The wound healed well and there was no recurrence or metastasis after 12 months of follow-up.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

EPs are benign adnexal tumors originating from the terminal portion of eccrine sweat gland ducts (1). The etiology of EP remains unclear, but factors such as chronic sun exposure, trauma, infection, inflammation, genetic mutations, and hormonal influences have been implicated (2). Clinically, EP presents as solitary, asymptomatic, well-circumscribed, smooth or verrucous papules or nodules that range from skin-colored to red or brown. They are usually less than 2 cm in diameter and are slow growing or fixed in size, and may occasionally ulcerate or bleed due to trauma or infection (1).

While EP typically occurs on acral sites like the palms and soles, involvement of the nail unit is rare (5-7). The atypical presentation of periungual EP can mimic other conditions, such as ingrowing toenail (5), verruca (6), or Bowen disease (7), making clinical diagnosis challenging.

Histopathologically, EPs are characterized by broad anastomosing bands of cuboidal cells with eosinophilic cytoplasm, solid nests, or duct-like structures filled with luminal eosinophilic material. Four histopathological variants depending on the localization of poroid cells have been reported: hidroacanthoma simplex (HS), EP sensu stricto, dermal duct tumor (DDT), poroid hidradenoma (PH) (8). The absence of atypia, mitosis, necrosis, or invasion, along with normal overlying epidermis and lack of junctional activity typically distinguishes EP from malignant tumors. Some scholars have reported the characteristics of dermatoscopy and reflectance confocal microscopy of EP, which might be helpful for clinical diagnosis (9,10). Line-field confocal optical coherence tomography (LC-OCT) is a novel technology able to reproduce a “virtual biopsy” of the skin, which is also might be helpful (11).

In this case, the lesion’s clinical appearance raised concerns for malignant neoplasms like amelanotic melanoma, as these can present as erythematous or pink macules, plaques, or nodules with irregular borders around the toenail (12). Differential diagnoses such as pyogenic granuloma, keratoacanthoma, and basal cell carcinoma were also considered. The definitive diagnosis of EP was made after histopathological and immunohistochemical analysis, highlighting the importance of biopsy in evaluating suspicious periungual lesions.

Complete surgical excision is the treatment of choice for EP, ensuring a definitive diagnosis and reducing the risk of recurrence or malignant transformation (1). Other treatment modalities, including cryotherapy, electrocautery, laser ablation, or topical agents like imiquimod, have been reported for smaller or superficial lesions (13), though their efficacy and safety remain uncertain.

The limitation of this report is that this situation was derived only from one patient. Further reports of similar cases might provide more robust evidence.

Conclusions

In a word, periungual EP is a rare entity that may present a diagnostic challenge. It may be mistaken for other benign or malignant lesions, such as amelanotic melanoma, which has a worse prognosis and requires a different treatment approach. Therefore, clinicians should be vigilant in considering this diagnosis and perform a biopsy for any suspicious periungual lesion. Early detection and accurate diagnosis are crucial for appropriate management and optimizing patient outcomes.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://cco.amegroups.com/article/view/10.21037/cco-24-94/rc

Peer Review File: Available at https://cco.amegroups.com/article/view/10.21037/cco-24-94/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://cco.amegroups.com/article/view/10.21037/cco-24-94/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration (as revised in 2013). Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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