Key point in dermoscopic differentiation between early nail apparatus melanoma and benign longitudinal melanonychia

Longitudinal melanonychia presents in various conditions including neoplastic and reactive disorders. It is much more frequently seen in non-Caucasians than Caucasians. While most cases of nail apparatus melanoma start as longitudinal melanonychia, melanocytic nevi of the nail apparatus also typically accompany longitudinal melanonychia. Identifying the suspicious longitudinal melanonychia is therefore an important task for dermatologists. Dermoscopy provides useful information for making this decision. The most suspicious dermoscopic feature of early nail apparatus melanoma is irregular lines on a brown background. Evaluation of the irregularity may be rather subjective, but through experience, dermatologists can improve their diagnostic skills of longitudinal melanonychia, including benign conditions showing regular lines. Other important dermoscopic features of early nail apparatus melanoma are micro-Hutchinson's sign, a wide pigmented band, and triangular pigmentation on the nail plate. Although there is as yet no solid evidence concerning the frequency of dermoscopic follow up, we recommend checking the suspicious longitudinal melanonychia every 6 months. Moreover, patients with longitudinal melanonychia should be asked to return to the clinic quickly if the lesion shows obvious changes. Diagnosis of amelanotic or hypomelanotic melanoma affecting the nail apparatus is also challenging, but melanoma should be highly suspected if remnants of melanin granules are detected dermoscopically.     

Key points in dermoscopic differentiation between lentigo maligna and solar lentigo

A clinical diagnosis of lentigo maligna at an early stage is often difficult even for experienced dermatologists. Differential diagnoses would include solar lentigo, early lesions of seborrheic keratosis, lichen planus-like keratosis, pigmented actinic keratosis and melanocytic nevus. Dermoscopy has been shown to have higher diagnostic accuracy, especially in the diagnosis of pigmented skin lesions, in the past two decades. To aim of the present study was to review the diagnostic key points on dermoscopy in the published work to differentiate lentigo maligna from other differential diagnoses and reassess these important features on dermoscopy for specificity by describing the findings in detail. Diagnostic key points for lentigo maligna/lentigo maligna melanoma on dermoscopy are asymmetrical pigmented follicular openings, rhomboidal structures, annular-granular structures and gray pseudo-network. Lentigo maligna, at first, seems to occur as asymmetrical pigmented follicular openings and/or annular-granular structures, then expand and develop into the rhomboidal structures. Annular-granular structures and gray pseudo-network seem to be observed also in regressive areas of solar lentigo/initial seborrheic keratosis, lichen planus-like keratosis and pigmented actinic keratosis. The four important criteria on dermoscopy for the diagnosis of lentigo maligna have been reviewed, and the former two criteria seem to be more specific, but it might be difficult to recognize these findings without misinterpretation. The latter two seem to be not so specific as they would also be demonstrated in other pigmented epidermal lesions, although the distribution of the structures in these disorders would be inclined to be more homogeneous than that of lentigo maligna.     

Key points in the dermoscopic diagnosis of hypomelanotic melanoma and nodular melanoma

Nodular melanoma (NM) and amelanotic/hypomelanotic melanoma (AHM) often present a challenge to the diagnosing clinician. A significant proportion of AHM are nodular in nature. Such tumors may lack features of asymmetry and altered peripheral pigmentation routinely observed in other melanoma subtypes. This lack of distinguishing clinical features can potentially result in delayed diagnosis or inappropriate treatment. This review highlights the key points in evaluating the range of lesions where AHM or NM are considered in the differential diagnosis and summarizes current evidence in relation to pigmented and vascular dermoscopic diagnostic criteria for both.     

Characteristic distribution of melanin columns in the cornified layer of acquired acral nevus: an important clue for histopathologic differentiation from early acral melanoma

Clinical and histopathologic differentiation between early acral melanoma and acral nevus is often difficult. Dermoscopy is helpful in this differentiation. On dermoscopy, early acral melanoma shows the parallel ridge pattern showing band-like pigmentation on the ridges of the surface skin markings, whereas a representative dermoscopic pattern in acquired acral nevus is the parallel furrow pattern showing parallel linear pigmentation along the surface furrows. The parallel furrow pattern suggests that melanocytes of acral nevus preferentially proliferate in the crista profunda limitans, an epidermal rete ridge underlying the surface furrow. In the present study, however, we found that in 13 of 18 acquired acral nevi, proliferation of melanocytes were detected not only in the crista profunda limitans but also in the crista profunda intermedia (CPI), an epidermal rete ridge underlying the surface ridge. Very interestingly, Fontana-Masson staining of these acral nevi revealed that even when proliferation of melanocytes was prominent in the CPI, melanin granules in the cornified layer were observed as regular melanin columns situated under the surface furrows and were hardly detected under the surface ridges. These findings indicate that in acral nevus, melanin granules produced by melanocytes in the CPI are not transferred to the upper epidermis. Hence, we must be careful not to overdiagnose an acral melanocytic lesion in which an increased number of melanocytes are detected in the CPI. Even in such a case, if melanin granules in the cornified layer are detected as melanin columns regularly distributed under the surface furrows, the lesion is strongly suggested to be a benign acral nevus.     

Epidermolysis bullosa nevus: an exception to the clinical and dermoscopic criteria for melanoma

BACKGROUND: Large acquired melanocytic nevi that occur in patients with epidermolysis bullosa (EB), referred to as EB nevi, may pose a diagnostic challenge because of their clinical and dermoscopic resemblance to melanoma. These unconventional melanocytic nevi have been encountered in all categories of hereditary EB, most of them in childhood. Although some of the reported cases have an alarming clinical appearance that is indistinguishable from melanoma, long-term follow-up has confirmed the benign nature of these rarely encountered melanocytic lesions. The histopathologic patterns of these nevi range from a banal congenital pattern to the problematic persistent pseudomelanoma pattern. OBSERVATION: We describe the clinical, dermoscopic, and histopathologic features of a large EB nevus in a toddler. Clinically, the lesion was markedly asymmetrical and irregularly pigmented with foci of stippled pigmentation and scarring, which easily fulfilled the ABCD criteria for melanoma. Accordingly, a false-positive score resulted when dermoscopy was performed. Histopathologically, a pattern of persistent melanocytic neoplasm was observed. In the following 18 months, dynamic changes of the lesion included near-complete disappearance of the pigment, which was replaced by scar, milia, and areas of healing ulcers. CONCLUSION: Epidermolysis bullosa nevi are dynamic melanocytic lesions that may simulate melanoma.     

Key points in dermoscopic diagnosis of basal cell carcinoma and seborrheic keratosis in Japanese

Basal cell carcinoma (BCC) and seborrheic keratosis (SK) are representative pigmented skin tumors, and they are differentiated as non-melanocytic lesions in the two-step dermoscopy algorithm proposed by the Consensus Net Meeting on Dermoscopy. Because most BCC in Japanese patients are pigmented clinically, dermoscopy plays an important role in their differential diagnosis. The dermoscopic criteria for BCC include the lack of a pigment network and the presence of at least one positive feature for BCC, such as large blue-gray ovoid nests, multiple blue-gray globules, leaf-like areas, spoke wheel areas, arborizing vessels and ulceration. Whereas various dermoscopic features are seen in SK, comedo-like openings, milia-like cysts, and fissures and ridges are especially important features. It is necessary for clinicians to consider the pathological conditions causing the dermoscopic features of BCC and SK. In addition, the sensitivity and specificity of each feature should be taken into consideration to ensure an accurate dermoscopic diagnosis.     

Immunohistochemical characterization of Spitz's nevus: differentiation from common melanocytic nevus, dysplastic melanocytic nevus and malignant melanoma

Recently it has been reported that Spitz's nevus possesses a deranged melanogenesis with formation of the spherical melanosomes also seen in superficial spreading melanoma (SSM) and dysplastic melanocytic nevus (DMN). To characterize the nature of Spitz's nevus, immunohistochemical studies were carried out in 9 cases of this condition using monoclonal antibodies (MoAbs) which identify (a) human melanosome-associated antigen (HMSA-1 and HMSA-2), (b) S-100 protein (α and β subunits), (c) Leu-7 (HNK-1), (d) β2 microglobulin (B2MG), and (e) neuron specific enolase (NSE). In contrast to SSM and DMN, none of the 9 cases showed any significant reactivity with MoAbs HMSA-1 and HMSA-2. Similar to cutaneous malignant melanoma (CMM) and DMN, and unlike common melanocytic nevus (CMN), anti-S-100 protein α subunit MoAb reacted from moderately to intensely with Spitz's nevus, and anti-S-100 protein β subunit MoAb reacted weakly. Anti-B2MG MoAb was reactive with 8 of 9 cases. Only one case showed cytoplasmic reactivity to anti-Leu-7 MoAb. Polyclonal NSE was found in 7 cases at varying intensities. Our immunohistochemical study indicates the distinct, benign neoplastic nature of Spitz's nevus which has immunoreactivities differing from those of CMM, DMN and CMN.     

Clear cells in acral melanoma

Acral melanoma may present clinically and histologically with atypical features causing a delay in proper diagnosis. The aim of the present study was to assess the frequency of a histological variant with clear cell changes. Clinical information, hematoxylin & eosin stained paraffin sections and immunohistochemical staining profiles were reviewed in 49 cases of acral melanoma. Twenty-one (43%) specimens contained tumor cells with clear cell changes in focal areas, whereas in 7 (14%) specimens clear cells were the major tumor constituting cells. The tumor thickness ranged from melanoma in situ to 14 mm. Immunohistochemistry demonstrated weak staining for S100 and HMB45 as well as strong positivity for Melan A and NK1C3. Recognition of clear cell features is important since differential diagnosis includes a variety of other clear cell malignancies, among them metastasis from renal cell carcinoma, clear cell sarcoma and hidradenocarcinoma.     

Acquired agminated melanocytic nevus in the acral area is a potential mimicker of acral lentiginous melanoma: A three-case series report and published work review

Agminated nevus refers to a clustered group of melanocytic nevi confined to a localized area of the body. It rarely involves acral skin, but recognition of acquired agminated nevus (AAN) in the acral area is clinically important because it may mimic acral lentiginous melanoma (ALM). However, acral AAN has only been described in a few case reports and its clinical characteristics remain unclear. We report three additional cases of acral AAN to further analyze the differential points between ALM. Clinical images, including those of dermoscopy, of three cases of acral AAN were reviewed. The lesions were located on the sole or lateral border of the foot. All acral AAN were flat and large in size (>20 mm in greatest dimension), and associated with asymmetry and irregular border. However, no parallel ridge pattern suggesting ALM was observed on dermoscopy. In two patients, the lesions on the sole were totally resected; microscopic evaluation of these two lesions confirmed junctional nests of banal melanocytes. AAN lesions on the sole with chronic mechanical pressure are slightly larger and more diffuse; thus, they may be more likely to be overdiagnosed as malignancy upon inspection than those in the non-acral area. Understanding the concept of the disease and careful dermoscopic evaluation leads to an accurate diagnosis.     

Significance of dermoscopic patterns in detecting malignant melanoma on acral volar skin: results of a multicenter study in Japan

OBJECTIVE: To determine diagnostic variables such as sensitivity and specificity of the major dermoscopic patterns observed in melanocytic lesions on acral volar skin, with particular attention to the significance of the parallel ridge pattern and irregular diffuse pigmentation in detecting acral melanoma. DESIGN: Multicenter, retrospective study. SETTING: University hospitals in Japan. PATIENTS: Patients with melanocytic lesions on acral volar skin. A total of 712 melanocytic lesions (103 malignant melanomas, including 36 in situ lesions, and 609 melanocytic nevi) were consecutively collected from the files of 3 hospitals. Diagnoses of all the lesions had been determined histopathologically. INTERVENTIONS: Dermoscopic examination. MAIN OUTCOME MEASURES: The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of the major dermoscopic patterns seen in benign and malignant melanocytic lesions on acral volar skin. RESULTS: The parallel ridge pattern and irregular diffuse pigmentation showed extremely high specificity (99.0% and 96.6%, respectively) and very high negative predictive value (97.7% and 97.5%, respectively) in malignant melanoma. For melanoma in situ, the positive predictive value and diagnostic accuracy of the parallel ridge pattern were significantly higher than those of irregular diffuse pigmentation (P = .009 and P = .006, respectively). In melanocytic nevi, the specificity and positive predictive value of the parallel furrow pattern and/or the latticelike pattern were found to be very high (93.2% and 98.3%, respectively). CONCLUSIONS: Dermoscopy is immensely helpful in differentiating malignant melanomas from melanocytic nevi on acral volar skin. Moreover, the parallel ridge pattern aids in detecting acral melanomas in early, curable stages.