Introduction
One of the great masqueraders in dermatology is amelanotic melanoma (AM). Most dermatologists have difficulty diagnosing these tumors since they are devoid of pigment. It has been previously estimated that a significant percentage of all melanomas are amelanotic.1 It has also been shown that AMs are often more advanced at diagnosis leading to a poorer prognosis.2 This is explained in part by the fact that there is often a delay in diagnosis due to uncharacteristic morphologies.2 Herein we present a new case of AM presenting as a pink plaque and review the dermoscopic findings to help make this difficult diagnosis.
CASE REPORT
The patient is an 84-year-old female who presented to the dermatology clinic complaining of a relatively new pruritic “rash.” She noted the rash had been present for three months and the itch was not relieved by over the counter topical steroids. She had a past history of basal cell carcinoma and squamous cell carcinoma insitu with a background of sun damage. On exam, she was a well appearing female with red hair and Fitzpatrick type I skin. There was a 1.1x0.4cm ill-defined, pink thin plaque on the left upper back (Figures 1 and 2). It was thought this was a superficial basal cell carcinoma based on clinical exam. A shave biopsy was performed. The dermatopathologist concluded it was an amelanotic melanoma. The Breslow thickness was 1.0mm. There was no ulceration and one mitotic figure per high power field. The patient was referred to surgical oncology for wide excision and sentinel lymph node biopsy which was negative. The patient continues to be monitored with full skin exams and subsequently in the following year and a half had not developed evidence of recurrence.
DISCUSSION
AMs do not represent the common pigmented form of melanoma and they can resemble other benign or malignant lesions giving a wide differential diagnosis. The differential diagnosis for AM includes intradermal nevi, scars, patch of eczema, actinic keratosis, Bowen’s disease, as well as basal cell carcinomas to name a few.3 Dermoscopy is a great tool in diagnosing AMs but does not make the diagnosis definitive. There are several dermoscopic features that have been described to be associated with amelanotic melanomas. These are polymorphous vessels, multiple blue-gray dots, blue-white veil, asymmetric shape, multiple colors, milky red areas, and scar-like depigmentation.4-6 Some have advocated that dotted vessels in association with linear irregular vessels are a more specific morphology4-6 and scar-like depigmentation is also more predictive.4,5 Important dermoscopic features that argue against AMs are symmetrical shape, multiple milia-like cysts, multiple blue-gray globules, and predominantly comma or arborizing vessels.5 Table 1 highlights these important dermoscopic findings.In our case, AM was not on the clinical differential diagnosis initially but the plaque did have polymorphous vessels consisting of dots and hairpin vessels. Our patient had Fitzpatrick type I skin and red hair, which has been previously associated with increased risk of melanoma.7 In our case, there was not a long delay to diagnosis. However, the tumor was already one millimeter in depth. This case supports a previously described theory that AMs are inherently more aggressive and associated with poorer prognosis.2 The key to diagnosing these tumors is maintaining a high index of suspicion. A low threshold to
