Rash orientation in pityriasis rosea: a qualitative study.

Rash orientation in pityriasis rosea (PR) has been described as Christmas-tree pattern, inverted Christmas-tree pattern, fir tree pattern, parallel to the ribs or along skin cleavage lines. We retrieved clinical photographs of 11 patients diagnosed as having PR over a two-year period for qualitative study of rash orientation. We found that Langer's cleavage lines are the most appropriate description. All three components of these lines on the trunk, i.e. V-shaped pattern on upper chest and upper back, circumferential pattern around the shoulders and hips, and transverse pattern on the lower anterior trunk and lower back, are demonstrated by most patients. We believe with the present state of knowledge, the mechanism for PR following Langer's lines is best considered unknown. We advocate abandoning other descriptions which might cause confusion to students and trainee physicians.