A male patient in his fourth decade of life presented to the clinic for evaluation of psoriasis. Dermatoscopy of a lesion on the right posterior upper arm that clinically resembled a psoriasiform papule showed numerous polarizing-specific white lines and polymorphous vessels ( Figures 1, A–C ). Dermatoscopy of nearby papules and plaques of psoriasis revealed white scale on a background of randomly distributed dotted and coiled vessels ( Figure 1D ). The lesion in Figure 1A was sent for histological analysis and found to be a malignant melanoma with a Breslow depth of 0.7 mm, occurring in association with a nevus.
Figure 1 .
(A) Clinical image of the patient right upper arm with scattered pink papules and plaques with overlying white scale. (B) Close-up image of the patient right upper posterior arm showing an 8 mm erythematous papule with white scale. (C) Dermatoscopic view showing many polarizing-specific white lines and polymorphous vessels (polarized dermatoscopy). (D) Dermatoscopic view of nearby psoriasis showing white scale on a background of randomly distributed dotted and coiled vessels (polarized dermatoscopy).
Though clinically the melanoma resembled a psoriatic papule, under dermatoscopy the lesion appeared very different from other psoriatic lesions and had features of melanoma. This highlights the importance of dermatoscopy and inflammoscopy in the diagnosis of neoplasms and inflammatory conditions. The most common dermatoscopic pattern of psoriasis is erythematous background with evenly distributed red dots and white scale [ 1 ] . Polarizing specific white lines and polymorphous vessels, clues that can be seen in melanoma, would not be expected in psoriasis [ 2 ] .
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