Unusual Clinical Presentations of Malignant Melanoma: A Review of Clinical and Histologic Features with Special Emphasis on Dermatoscopic Findings

Abstract

This review presents the main challenges encountered when diagnosing unusual variants of malignant melanoma with the aim of raising awareness to allow application of the most appropriate treatment strategies. Although these melanomas are often rare, their misdiagnosis potentially jeopardizes patients' health and survival, and has medicolegal implications. The clinical and histologic presentations of melanoma vary greatly, and assessment of uncommon melanomas can be difficult for practitioners because of their scarcity and resemblance to other dermatologic entities. The most problematic melanoma types are desmoplastic melanoma, polypoid melanoma, primary dermal melanoma, verrucous malignant melanoma, pigmented epithelioid melanocytoma, mucosal melanoma, follicular melanoma and melanoma with non-melanocytic differentiation. The two most difficult-to-diagnose subtypes of melanoma are the nevoid and the amelanotic melanomas. Some specific attributes of these variants can be more easily recognized with digital dermatoscopy, facilitating early detection and possibly avoiding invasive procedures. Key cases with the most notable clinical, dermatoscopic, and histopathologic features are presented, highlighting the practical issues of making an accurate diagnosis and choosing the best therapy.

Fig. 1

Images of desmoplastic melanomas (a-1 to b-2 from Chen et al. [13] and b-3 to b-4 from Debarbieux et al. [15]). a Pure type: a-1 close-up photograph of a firm cystic to scar-like nodule and a-2 dermatoscopy showing atypical dotted vessels (arrow). b Mixed type: b-1, b-3 close-up photograph, and b-2, b-4 dermatoscopy shows regression structures (box in b-2), dotted and arborizing vessels (arrows in b-2), a regression pattern ‘peppering’ (big arrow in b-4), linear irregular vessels (small arrows in b-4), and a white scar-like structureless area (asterisk in b-4)

Fig. 2

Images of four unusual subtypes of malignant melanoma. a Polypoid melanoma (Cabrera R, personal images). a-1 Close-up photograph of a 3-cm diameter, pedunculated pigmented lesion on the posterior trunk, in which the upper part is attached to the brown-blue pigmented skin with a colorless peduncle of only 0.5 cm. a-2 Dermatoscopy shows a blue-white veil in the exophytic lesion, and big blue-gray nests and whitish areas in the peduncle’s base. b Primary dermal melanoma (from Cabrera et al. [24]). b-1 Close-up photograph of a pigmented vascular lesion on the thorax. b-2 Dermatoscopy shows dark brown blotchy areas in some papillomatous projections (single arrow), areas with a light brown-pink color (double arrow), and a ‘blue-hue’ color without a veil (asterisk). c Verrucous malignant melanoma (Cabrera R, personal images). c-1 Close-up photograph of a verrucous lesion on the face. c-2 Dermatoscopy shows bluish-white veils with dots and globules, and peppering in some areas. d Pigmented epithelioid melanocytoma (from Aviles-Izquierda et al. [30]). d-1 Close-up photograph of a pigmented nodule on the arm. d-2 Dermatoscopy shows a homogeneous blue lesion with whitish structures, a blue-white veil, and polymorphic vessels

Fig. 3

Case report of a mucosal melanoma (Cabrera R, personal images). Progression over 4 years of a mucosal melanoma in the oral cavity of a 70-year-old woman. Pigmentation was present initially and the lesion changed rapidly. The patient initially refused the biopsy (1998) but 2 years later an examination confirmed it was a melanoma (2000). However, the patient decided not to be treated. In 2002, surgery was finally performed, and the sentinel lymph nodes appeared to be totally pigmented (not shown)

Fig. 4

Dermoscopic images of the three main groups of nevoid melanoma (a-1 to b-4 from Longo et al. [34]). a Nevus-like nevoid melanomas. All lesions show a nevus-like appearance with colors varying from skin-colored (a-1) to light brown (a-2), bluish (a-3) and reddish brown (a-4). Irregular pigmentation (a-1, a-3) and irregularly distributed globules (a-2, a-4) are observed. b Amelanotic nevoid melanomas. All tumors have an atypical vascular pattern, with either linear–irregular vessels or serpentine (b-1), dotted (b-2, b-3) or glomerular vessels (b-4). Multiple milia-like cysts can be seen (b-3). c Nevoid melanoma with a multicomponent pattern (Raúl Cabrera personal images). A delimited plaque of 1.2 × 1.5 cm shows a brown, black, slightly raised periphery and whitish center (c-1). Dermatoscop (c-2) shows linear projections at the periphery (black arrows) with brown dots and globules (*), chrysalis in the center (blue arrows) and arborizing vessels (thick blue arrow)

Fig. 5

Hypomelanotic melanoma (Cabrera R, personal images). a Chronic foot ulcer with a hypopigmented lesion. In the inset, the arrow shows the exclusively peripheral localization of the atypical pigmented area on a chronic foot ulcer. Dermatoscopy of this area shows an atypical red pigmentation on the periphery (arrow on the main image). b Biopsy of the lesion. The deep part of the dermis presents pigmentation (arrow)

Fig. 6

Follicular melanoma (Cabrera R, personal images). Punch biopsy showing atypical melanocytes surrounding the hair shaft