HN and vitiligo are probably two distinct entities involving separate, independent pathways leading to depigmentation, but a possible overlap might exist in a subset of patients. An immune response to nevocytic antigens that spills over to melanocytes can be speculated because of the frequency of HN in vitiligo patients as compared to the general population. Whether the presence of HN represents a risk factor for onset of vitiligo (Barona MI, Arrunategui A, Falabella R, Alzate A (1995)) or a sign of progression of active vitiligo is not yet settled.
The loss of pigmentation in HN is thought to be ant i-inflammatory/immunological process. The usual explanation of the depigmented ring is that the immunologic response, fi rst directed against the nevus melanocytic antigen(s), outgrows its first target to cause the loss of normal melanocytes of the surrounding skin. The halo around the nevus is always remarkably round or oval. This geometrical figure has led some authors to suggest a phenomenon beginning at the centre where the nevus is situated, and then spreading centrifugally around (De Vijlder HC, Werterhof W, Schreuder GM et al (2004)
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