Late recurrence of inflammatory first-stage lesions in incontinentia pigmenti: an unusual phenomenon and a fascinating pathologic mechanism.

BACKGROUND Incontinentia pigmenti (IP) is an X-linked genodermatosis that is manifested by neonatal inflammatory vesicles localized along the lines of Blaschko. These lesions usually clear spontaneously within a few months, leaving hyperpigmentation. Ophthalmologic and neurologic symptoms can be associated with IP. Late recurrences of the first-stage inflammatory lesions after the initial rash are uncommon and have been reported infrequently. The mechanism involved in this phenomenon is unclear. However, the recent identification of NEMO/IKKgamma as the gene responsible for IP sheds new light on its pathophysiologic origins. OBSERVATIONS We report 5 cases of children who experienced episodes of late reactivation of IP. In all cases, the recurrences occurred on the previously hyperpigmented streaks several months or years after resolution of the initial eruptions. In most cases, the recurrences were preceded by an infectious episode. CONCLUSIONS These IP recurrences suggest that mutated cells can persist a long time in the epidermis. We theorize that infections trigger the reactivations. The NEMO/IKKgamma gene encodes a protein essential in nuclear factor kappaB activation, which is required for resistance to tumor necrosis factor alpha-induced apoptosis. We discuss the role of a proinflammatory cytokine such as tumor necrosis factor alpha as a triggering factor for the reactivation.