IN ITS classic form, pityriasis rosea is a distinctive dermatosis and is readily identified clinically. A diffuse distribution of skin lesions over the trunk and proximal portions of the extremities is commonly seen. The individual lesions are typically annular and oval in shape, with their long axes parallel to the so-called lines of cleavage of the skin. On the trunk this can result in a dermatomal or segmental patterning sometimes referred to as a "Christmas tree" distribution. The face, scalp, distal extremities, volar skin, and mucous membranes are involved less frequently. However, an inverse form of pityriasis rosea with principal involvement of the face and extremities and relative sparing of the trunk may be seen occasionally.
Reference has been made to the occasional restriction of pityriasis rosea to certain areas, such as the lower trunk.1-4 The vulnerability of this portion of the skin surface was presumed due to its
Hurley HJ, English RS. Localized Pityriasis Rosea. JAMA. 1961;178(7):766–768. doi:10.1001/jama.1961.73040460036017d