The role of line‐field confocal optical coherence tomography (LC‐OCT) in the diagnosis of eccrine poroma: A case report

Poroma is skin cancer that arises from the sweat gland cells. Its diagnosis could be difficult. Line‐field optical coherence tomography (LC‐OCT) is a novel imaging technique that has shown promise in the diagnosis and monitoring of various skin conditions. We report a case of poroma diagnosed by LC‐OCT.


INTRODUCTION
Eccrine poroma (EP) is a rare benign adnexal neoplasm that typically presents as a solitary, dome-shaped papule or nodule, generally found on an acral location. These features overlap with various differential diagnoses, such as basal cell carcinoma, amelanotic melanoma and benign epithelial neoplasms.
This work aims to contribute to the present knowledge about the features of eccrine poroma found by line-field confocal optical coherence tomography (LC-OCT).

MAIN TEXT
A 73-year-old man presented to our clinic with a nodular lesion on the left ankle. Cutaneous examination revealed a well-circumscribed, sessile reddish nodule measuring 17 mm × 9 mm (Figure 1a).
Analysis of LC-OCT images revealed a welldemarcated lesion (Figure 2, Figure 3) composed of bright, homogeneous round islands surrounded by dark silhouette stroma; between tumoral proliferations, hyporeflective structures of various shapes and sizes within the dermis corresponding to vascular proliferation could be observed.
Some tumoral nodules were in direct relation to the epidermis, which appeared stretched towards the dermis.
The tumoral cellular component was composed of small round cells with hyporeflective nuclei. A clear separation was evident between these cells and keratinocytes, which showed a honeycomb pattern (Figure 2c,d, Figure 3).
Based on the clinical, dermoscopic and LC-OCT findings, a diagnosis of eccrine poroma was hypothesized.
Histopathology exam from excisional biopsy displayed well-circumscribed multiple solid round nodules of poroid cells within the dermis, with a nonpalisading pattern. No presence of foci of porocarcinoma was signalled ( Figure 1c).
Differential diagnosis between eccrine poroma and several dermatologic conditions may be difficult even for an expert dermatologist. An accurate evaluation of the patient presenting with poroma is consequently mandatory, and different not invasive techniques are used in this field. Some authors report the usefulness of dermatoscopy in the diagnosis of poroma. The main dermatoscopic features documented are round-to-oval pink areas surrounded by peripheral white interlacing white cords. The vascular pattern is often polymorphous combining hairpin, dotted and linear irregular vessels, while coiled, glomerular and leaf-like vessels are less frequently found. 1,2 By contrast, it must be considered that eccrine poroma presents a significant dermatoscopic variability simulating another benign or malignant disease such as melanoma, Bowen disease, squamous cell carcinoma or seborrheic keratosis. 3 The use of reflectance confocal microscopy (RCM) can be a different, not invasive approach to the diagnosis of poroma. Indeed, RCM examination may show features such as cords without palisading, dark holes, prominent vascularization and abundant stroma that seem more associated with a diagnosis of EP. 4 This technique allows a rapid evaluation and offers an excellent image resolution but has a lower penetration and cannot correlate the obtained images directly with dermoscopy.
By contrast, LC-OCT technology has a superior penetration in depth (up to 500 μm), creating vertical similar 'histological' sections and 3D reconstructions of the examined tissue. In our case, this technique allowed us to highlight and correlate these images with certain typical histological aspects. Figure 2 and Figure 3 shown a nodular mass growing from the epidermis with a monomorphic small cellular population. There is a sharp demarcation between the keratinocytes of the adjacent epidermis and cuboid cells of poroma and clear poroid differentiation.
Even if the diagnosis of EP is made by histopathology, LC-OCT examination can rule out classical patterns of malignant tumours such as melanoma and basal cell carcinoma. Indeed, in our case, the LC-OCT features were not indicative of melanocytic proliferation due to the absence of irregular honeycombed pattern, pagetoid spread and dermal nests at vertical view. 5 Furthermore, branched lobules with the peculiar millefeuille pattern surrounded by a dark rim were not evident, and on these grounds, diagnosis of basal cell carcinoma was excluded. 6 Although EP is a benign tumour, approximately 18% of poromas went on to become porocarcinomas, with an average time of progression to malignancy of 8.5 years. 2 Porocarcinoma is generally characterized by tumour nodules in correlation with the epidermis but with more deep margins, infiltrative aspects and atypical poroid cytology. As a consequence, at LT-OCT examination, this lesion may show deeper nodular lesions composed of poroid cells of different sizes, but as yet no case has been reported in the literature.

CONCLUSION
In conclusion, we report a case of eccrine poroma evaluated with LC-OCT. This technique allows a rapid assessment with a quasihistological resolution, helping the choice of proper management in benign skin cancers such as poroma. Additional studies are needed to investigate this field and to confirm our evidence.