Benign Dermoscopic Parallel Ridge Pattern Variants

Abstract

T HE PARALLEL RIDGE PATTERN (PRP) IS A VOlar dermoscopic pattern that is characterized by an accentuated pigmentation on the ridges of the skin markings, while the furrows are hypopigmented or unpigmented. It has been demonstrated to be highly specific for acral melanoma, and its presence must be considered a warning sign of melanoma. However, rare cases of benign acral melanocytic nevus can exhibit the PRP, as in the edge of the compound melanocytic nevus shown in Figure1A. The acral blue nevus (Figure 1B) usually shows a bluish, quite homogeneous pigmentation involving the ridges. Ethnic pigmentation clinically presents as pigmented macules with a typical PRP on the palms and soles (Figure2A). The multiplicity, bilateral location, and chronicity of the lesions are suggestive of ethnic-type pigmentation. The presentation is similar in Laugier-Hunziker or Peutz-Jeghers syndrome. Ectasic papillary capillaries of acral angioma present as regular red-blue globules along the ridges (Figure 2B). Repetitive microtrauma can cause extravasation of erythrocytes in the cornified layer, with subsequent misleading globular reddish brown pigmentation on the ridges, as seen in Figure 3A, which shows a posttraumatic purpura due to the friction of the fifth finger caused by regular use of the computer mouse. The PRP was also found in subcorneal hematoma. The lesion appears as well-demarcated roundish macule, with reddish brown pigmentation along the ridges (Figure 3B). Deposit of exogenous pigmentation on the ridges, especially in areas where the stratum corneum is thicker, can also simulate melanoma, as shown in Figure 4, with the use of a self-tanning preparation by a woman with localized palmar hyperkeratosis.