Abstract

Background: Amelanotic melanomas (AM), a rare subtype of melanoma characterized by lack of pigmentation, is a particular diagnostic challenge as they rarely demonstrate the ‘ABCDE’ criteria (Asymmetry, Border irregularity, Color variegation, Diameter >6 mm, and Evolution) used for melanoma screening. AM may present as skin-colored, pink, or erythematous, among which erythematous AMs account for nearly 70% of AMs. As a result, AM may be misdiagnosed as pyogenic granuloma, hemangioma, basal cell carcinoma, Bowen’s disease, eczema, or keratoacanthoma. Importantly, the prognosis of AM is similar to that of pigmented melanomas, so delays in diagnosis can lead to worse prognoses for patients. Case Presentation: A 58-year-old non-Hispanic white male presented with a growing erythematous nodule, measuring 1.7 x 1.0 cm, on his left arm that had been present for at least a year. The clinical diagnosis was pyogenic granuloma vs other, and a shave biopsy of the lesion was taken. To our surprise, the histology revealed a nodular proliferation of atypical melanocytes present throughout all layers of the epidermis extending into the deep dermis, with an approximate depth of 3.2 mm. Conclusion: Amelanotic melanoma (AM) is a particular diagnostic challenge, as it does not exhibit the same characteristics as its pigmented counterpart. However, prognosis is similar to that of pigmented melanomas, so early detection and excision is important. AMs may range from skin colored to red, with many presenting as erythematous lesions that resemble other dermatologic conditions. Due to the potential for misdiagnosis, an adult patient presenting with a new erythematous nodule that looks like a pyogenic granuloma should be biopsied.

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