Vitiligo and Psoriasis: A Possible Coexistence?

The vitiligo and psoriasis are common skin diseases with prevalences estimated at 0.5-2% and 2-4% respectively. From a clinical perspective, vitiligo is a depigmenting dermatosis characterised by well-defined white patches, varying in size across the skin. Regarding the psoriasis, its manifestations can differ depending on its form, but, in 90% of cases, it involves circumscribed erythematous and scaly plaques. The association of vitiligo and psoriasis has been described since the 19thcentury in epidemiological studies. The results of one of these are presented below. The coexistence between psoriasis and vitiligo can be explained by the numerous shared genetic predisposition factors between these diseases, as well as common pathophysiological and immunological mechanisms, such as the Koebner phenomenon.

Indeed, a recent bioinformatic analysis conducted on lesion and non-lesion skin tissues from patients suffering from psoriasis and vitiligo has enabled the identification of several potential genes associated with psoriasis and vitiligo. These include AKR1B10, which is overexpressed in these conditions, and FOXC1, KIT, MLPH and SOX10, which are underexpressed. These genes are involved in various processes, notably immune and inflammatory ones. However, their pathogenic mechanisms are not fully understood. Another study suggested that a genetic polymorphism on the AIS1 gene could also be associated with vitiligo and psoriasis and may also promote other autoimmune diseases.

The association between vitiligo and psoriasis is also based on an immunological foundation, particularly on the infiltration of CD8+ T lymphocytes into the melanocytes. These lymphocytes are often found in psoriasis plaques, where they cause chronic inflammation. Indeed, some studies suggest that an infiltrate of CD8+ T lymphocytes targeting melanocytes can not only contribute to the pathogenesis of psoriasis, but also to that of vitiligo, by triggering the destruction of melanocytes. This loss of melanocytes is the cause of the depigmentation observed in patients with vitiligo, as these are the cells that produce the melanin, the brown pigment that colours the skin. These observations help to explain why psoriasis often precedes vitiligo and acts as a triggering factor.

Finally, another intriguing aspect of the pathogenesis of psoriasis and vitiligo is the emergence or worsening of lesions following trauma, a process known as the Koebner phenomenon. This phenomenon, also referred to as an isomorphic reaction, describes the induction of lesions on the unaffected skin of patients following any form of skin trauma. The exact pathogenesis of the Koebner phenomenon is not yet fully understood. Consequently, it is not uncommon to see vitiligo and psoriasis lesions coexisting in areas frequently subjected to friction, such as the elbows or knees.

It is entirely possible for vitiligo and psoriasis to coexist. Most often, psoriasis appears before vitiligo and the patches overlap.

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