Pigmented epithelioid melanocytoma: clinical, dermoscopic and histopathological features

Dear Editor, Pigmented epithelioid melanocytoma (PEM)1 is a recently proposed term that encompasses melanocytic tumours showing overlapping features between an atypical epithelioid blue naevus (first described in Carney complex and then also as sporadic)2 3 and a low‐grade ‘animal‐type melanoma’ or ‘pigment‐synthesizing melanoma’.4 5 Clinically, PEM occurs over a broad age range, with a predilection for children and young adults.1 6 7 Histopathologically, it is characterized by a dermal proliferation of heavily pigmented, both dendritic and spindle/epithelioid melanocytes, admixed with slightly larger, plumper and less pigmented epithelioid cells.1 Involvement of the regional nodes has been reported in up to 46% of cases, but usually with no further spread of the disease.1 6 7 8 No histological criteria are predictive of metastatic behaviour.1 Thus, the tumour could be a low‐grade, lymphotropic variant of melanoma with frequent lymph node metastases but an indolent clinical course.1 6 7 8 The dermoscopic features of these uncommon skin tumours have not been described up to now. The aim of our study was to analyse the clinical, dermoscopic and histopathological features of a series of PEMs retrospectively collected, and to correlate the histological and dermoscopic features of these rare skin neoplasms. We retrospectively searched the image database of the ‘Gaetano Rummo’ General Hospital of Benevento, and Arcispedale Santa Maria Nuova, Reggio Emilia, Italy from 2004 to 2014 for images of excised tumours using ‘pigmented epithelioid melanocytoma’ as the keywords. All histopathological specimens were reviewed by two of us (R.R. and G.F.) on the basis of the criteria described by Zembowicz et al.1 Clinical and dermoscopic images were reviewed in agreement by two observers (E.M. and G.A.). Lesions were defined clinically as macular, papular and nodular. Dermoscopic criteria were evaluated on the basis of the most common dermoscopic criteria.9 Nine excised skin lesions with a histopathological diagnosis of pigmented epithelioid melanocytoma were found. The collected patients’ demographics and clinical information are summarized in Table 1. Their ages ranged from 3 to 57 years, mean 20 years. The majority of lesions were located on the head/neck area (n = 4), followed by lower limbs (n = 3), the upper limb (n = 1) and the dorsal aspect of the foot (n = 1). The majority of lesions were nodular (n = 6). Dermoscopically, all lesions showed a homogeneous blue pigmentation. Three cases presented blue and black colour (cases 3, 4 and 6). White colour, present as crystalline structures, was detected in cases 4 and 9. Brown colour and comedo‐like openings were detected in case 3. The dermoscopic differential diagnosis was melanoma in six cases and blue naevus in three (cases 1, 5 and 9) (Fig. 1). Clinical data, dermoscopic features and differential diagnosis of the cases in our series Sentinel node biopsy positive. Clinical data, dermoscopic features and differential diagnosis of the cases in our series Sentinel node biopsy positive. (a–e) Pigmented epithelioid melanocytoma (PEM) with melanoma‐like features. (a) Dermoscopy (×10) and clinical appearance (insert) of a pigmented nodule located on the chin of a 21‐year‐old man (case 4). The lesion is heavily pigmented with the presence of blue and black pigmentation in the centre, and crystalline structures at the periphery. (b–e) Histopathology: the neoplasm is heavily pigmented and nodular (b, HE ×20) with a broad grenz zone (c, HE ×40) and is composed of a combination of epithelioid cells, dendritic cells and melanophages (d, HE 100 ×), with occasional mitotic figures (e, circle, HE ×250). (f, g) PEMs with ‘lymphotropic’ features (cases 6 and 8). Dermoscopy (×10) of a PEM arising on the ear of a 3‐year‐old boy (case 8). The lesion is characterized by homogeneous blue pigmentation. A bluish pigmentation is clinically visible in vessel‐like structures surrounding the tumour, most probably lymphatic vessels (arrows). (g) A pigmented nodule arising on the lower limb of a 9‐yearold girl (case 6) (dermoscopy 10×). The lesion exhibits homogeneous blue pigmentation, black streaks and crystalline structures. At the ‘periphery of the lesion, three macules of homogeneous blue pigmentation are visible (arrows), histopathologically corresponding to satellite nodules with the same characteristics as the main tumour. Histopathologically, all of the neoplasms were dermal based, medium to large sized, more or less wedge shaped and heavily pigmented because of a proliferation of spindle/epithelioid and dendritic melanocytes admixed with many melanophages. No case showed a nested junctional component, but three cases disclosed a pigmented parakeratosis; in one of these cases (case 6), intraepidermal dendritic cells were found to be arranged in single units. A narrow grenz zone was seen in three cases, clinically mimicking a blue naevus. In case 1, sparse epithelioid cells with a striking pleomorphism were seen. Two cases (2 and 8) showed intralymphatic complexes of melanocytes. Necrotic areas were not detected; only occasional mitotic figures were found in three cases, but the immunostain for the cell‐cycle‐related protein Ki67 was very low in all cases. A sentinel node biopsy was performed only in case 7 and was positive for subcapsular microaggregates of melanocytes. In this case no completion lymph node dissection was carried out. Follow‐up data (range 1–7 years; mean 3·5) are uneventful to date. No correlation between histological and clinical and dermoscopic atypia was found in our cases. All cases presented a certain degree of cytological atypia, even if dermoscopically some of them presented a blue‐naevus‐like appearance. All cases were histologically dermal based, including those appearing as macular or only slightly palpable clinically. The presence of intraepidermal dendritic cells arranged in single units was found in case 6, exhibiting blue and black pigmentation in dermoscopy. Black pigmentation was visible in those cases presenting pigmented parakeratosis in histology. To the best of our knowledge, this is the first description of the dermoscopic features of PEM. In agreement with previous studies,1 6 7 8 our cases were found mainly in young patients (mean age 20 years) as nodular lesions, all exhibiting blue colour both clinically and dermoscopically (Table 1). However, PEM appear to present as polymorphic lesions dermoscopically, characterized by homogeneous blue pigmentation and a variable combination of black, brown and white colour.10 11 This description suggests a differential diagnosis from common blue naevus and melanoma.10 11 12 Structureless blue was the sole dermoscopic feature in three cases (Fig. 1). In those cases exhibiting only a structureless blue pigmentation, or homogeneous blue and crystalline structures, the lesions were excised because they were reported as growing.10 11 12 In the other cases, the combination of blue and black colour was the key feature that led to excision. In fact, this combination of colours, when present in nodular lesions, has been associated with the diagnosis of nodular melanoma (Fig. 1).11 13 Thus, even if we found no specific dermoscopic features of PEM, by combining clinical and dermoscopic criteria the chances of leaving these tumours untreated are very low. The question of the real biological significance of this spectrum of melanocytic lesions is still a matter of debate. In spite of the common regional node involvement, a true malignant behaviour has been reported only rarely, mainly as involvement of the regional nodes. Interestingly, one case in our series had a positive sentinel node biopsy (case 7). Even more interestingly, three spots of macular homogeneous pigmentation were visible close to the PEM in case 6; histologically these areas corresponded to satellite nodules with the same histological characteristics as the bulk of the tumour. In one case a bluish pigmentation was clinically visible in vessel‐like structures surrounding the tumour, most probably lymphatic vessels (case 8). These clinicodermoscopic features are in keeping with the ‘lymphotropic’ properties of PEM (Fig. 1). In conclusion, PEMs present mainly as nodular tumours always exhibiting blue pigmentation; black, brown and white pigmentation can be variably present. No correlation between histological and dermoscopic atypia was found in our series. Larger case series are needed to confirm and expand these findings. Funding sources: This study was supported in part by the Italian Ministry of Health (RF‐2010‐2316524). Conflicts of interest: none declared.