Skin diseases following a Christmas tree pattern.

Pattern analysis of skin lesions is an art and a key competence of every dermatologist. Three major line patterns cover the human body-the dermatomes or Head zones, the nevoid lines of Blaschko, and the relaxed skin tension lines, or Langer lines. Head zones represent skin areas innervated from the same sensory neuronal segment or spinal nerve zone. Blaschko lines are borderlines of epidermal aberration caused by genetic mosaicism occurring in the early stages of embryogenesis. Langer lines show the direction of the lowest naturally occurring skin tension, and its thoracodorsal manifestation is the Christmas tree pattern. Here we review clinical aspects of pityriasis rosea, mycosis fungoides, stage 2 syphilis, exanthematic Kaposi sarcoma, exanthematic psoriasis, Leser-Trelat syndrome, and other primary skin diseases with a Christmas tree pattern. Secondary skin diseases, such as herpes zoster or indeterminate cell histiocytosis, may follow this pattern if they are linked to a primary skin disease by the Wolf isotopic response.