First transmission electron micrograph of continuous mitotic spindle fibers between polar area and chromosome ends

Congenital and/or nevoid skin disorders following the lines of Blaschko may have a delayed onset after birth. They have to be differentiated from acquired dermatoses exhibiting the same linear pattern. In common dermatoses, such as psoriasis or lichen planus, lesions in a blaschkolinear distribution most often occur together with scattered lesions, but occasionally they may be isolated. Less common self-limited dermatoses such as lichen striatus and adult blaschkitis always present in a blaschkolinear fashion. In these diseases, or some other conditions occasionally distributed along these lines (chronic graft versus host reaction, fixed drug eruption, lupus erythematosus, atopic dermatitis, etc.), the cause of the disease may lead to the unmasking of tolerance to an abnormal keratinocyte clone that remained hidden in these lines. In addition to epithelial cells, other cells may be involved in the occurrence of acquired blaschkolinear dermatoses. In linear atrophoderma and linear fibromatosis, the histogenesis seems to involve hypothetic dermal clones. The extension of an acquired dermatosis on a preexisting linear nevoid disorder is an argument in favor of an early embryonic somatic mutation of a skin cell line.