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 characterized by well-defined white patches, varying in size, on the skin. As for the psoriasis, its manifestations can differ depending on its form, but in 90% of cases, it presents as circumscribed erythematous and scaly plaques. The association of vitiligo and psoriasis has been described since the 19thcentury in epidemiological studies. The results of one such study are presented below. The coexistence of 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 with psoriasis and vitiligo has allowed 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, including immune and inflammatory responses. 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 colors the skin. These observations help explain why psoriasis often precedes vitiligo and acts as a triggering factor.

Finally, another interesting aspect of the etiopathogenesis of psoriasis and vitiligo is the appearance or worsening of lesions following trauma, a process known as the Koebner phenomenon. This phenomenon, also referred to as an isomorphic reaction, refers to the induction of lesions on the unaffected skin of patients following skin trauma, regardless of its nature. The exact pathogenesis of the Koebner phenomenon is not yet known to this day. Thus, it is not uncommon to see vitiligo and psoriasis lesions coexist on an area 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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• ZUBAIR M. & al. A case report showing coexistence of two autoimmune diseases-psoriasis and vitiligo. Journal of medical and allied sciences (2017).

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• KANG X. J. & al. Identification of key pathways and genes involved in psoriasis and vitiligo using bioinformatics analysis. International Journal of Dermatology and Venerology (2024).