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.

Cauliflower-like exophytic mass on the skin: polypoid melanoma. Clinical, dermoscopic, and histologic features

“… 1 Cabrera et al described a case of PM showing a blue-white veil in the exophytic part of the lesion and big blue-gray nests and whitish areas at the base of the stalk. 5 Accordingly to Hikawa et al, a clear dermoscopic analysis of the tumor can be impeded by the presence of crusts and fibers of clothing, gauzes, or patient's own hair, the so-called “fiber sign”, that is an indirect dermoscopic clue of ulceration. 6 …”

Small Cell Variant of Metastatic Melanoma: A Mimicker of Lymphoblastic Leukemia/Lymphoma

“…Melanomas are well-known for their variety of cytomorphological features, architectural patterns, and stromal changes. Signet-ring cell, small cell, metaplastic (chondroid, osteoid), myxoid, rhabdoid, and balloon cell are just some of the unusual cytomorphologic variants of melanoma [4]. They can mimic carcinoma, mesenchymal tumors, germ cell tumors, leukemia/lymphomas, plasmacytomas, and even benign stromal reactions and tumors [5].…”

A darkly pigmented verrucous papule on the nape of neck

“…Verrucous melanoma (VM) is one of the most challenging skin cancers to diagnose as it may be confused both clinically and histologically with benign lesions 1 . It is a rare variant of melanoma, accounting for approximately 3% of cases, and in 50% of these it is commonly misdiagnosed as a pigmented verrucous naevus, a compound or congenital naevus or a seborrhoeic keratosis (SK), with resultant delay in diagnosis and adverse impact on prognosis 2,3 …”