Intrinsic and extrinsic pathomechanisms in vitiligo

Vitiligo is the most commonly acquired hypomelanosis, and is restricted to a limited cutaneous territory (focal/segmental vitiligo [SV]) or generalized in symmetric patches (nonsegmental vitiligo [NSV]). In the majority of cases, vitiligo corresponds to a loss of melanocytes, first in the epidermal compartment, and later in the follicular reservoir where most melanocytic stem cells are probably situated. There are many data currently supporting an impaired redox status of the epidermal melanin unit as a primary defect leading to inappropriate immune responses in NSV. SV is probably a mosaic developmental predisposition to melanocytic loss, with similar mechanisms at work on a limited scale, as suggested by its cutaneous distribution and success of autografting. In NSV, engraftment of autologous melanocytes is less durable, especially in areas prone to repeated trauma or pressure. Although melanocytes are the obvious target of the disease, keratinocytes, as providers of antioxidant molecules to melanocytes as well as cofactors in the synthesis of melanin, are probably involved. The production of autoantibodies and specific cytotoxic T cells is not surprising in the context of the massive uptake of melanocytic antigens by Langerhans cells in unstable vitiligo vulgaris, thereby allowing the self-perpetuation of lesions. This article reviews the recent data on the pathophysiology of vitiligo, on the basis of clinical classification and the intrinsic/extrinsic nature of proposed pathomechanisms. Unfortunately, basic issues like pathological staging, clinical scoring, and eliciting factors have not yet been fully resolved. More genetic studies in vitiligo-prone families and in specific genetic disorders associated with vitiligo are also needed.