Efficacy of Topical Tyrosine Versus Topical 5-Fluorouracil With Fractional Erbium YAG Laser

Vitiligo is an autoimmune disorder affecting the skin, specifically targeting pigment-producing melanocytes, leading to noticeable regions of depigmentation characterized by white spots. Two major clinical forms of vitiligo are recognized: non-segmental vitiligo, the most common type, usually presenting with symmetrical lesions, and segmental vitiligo, which manifests as unilateral depigmentation.

The exact pathogenesis of vitiligo remains unclear. However, it is believed to be a complex process involving genetic susceptibility, metabolic disturbances related to oxidative stress, impaired melanocyte adhesion to the epidermis, and immune mechanisms including both innate and adaptive immunity, ultimately leading to selective melanocyte destruction. Nevertheless, none of these mechanisms alone can completely explain melanocyte loss, suggesting that vitiligo is a multifactorial disorder.

The management of vitiligo aims to halt disease progression, stimulate repigmentation, and prevent relapse, with repigmentation largely driven by melanocyte stem cells in hair follicles that can migrate and restore functional melanocytes to depigmented areas.

Immune modulators, such as topical steroids, topical calcineurin inhibitiors, phototherapies, and systemic therapy like oral steroids, are the mainstay of traditional treatments. However, these options are still not ideal, which prompts research into novel vitiligo treatments. There is still a need for workable and well-tolerated therapeutic choices, even if treatment must be tailored to each patient and particular lesions.

5-Fluorouracil (5-FU) is a hydrophilic pyrimidine analogue with significant anticancer activity and limited water solubility, first discovered in the 1950s by Heidelberger through the introduction of a fluorine atom at the fifth position of the uracil molecule.

Topical (5-FU) was first reported as a treatment for vitiligo where it stimulates the proliferation of melanocytes within hair follicles that subsequently migrate to the epidermis and contribute to vmelanin production.

Tyrosine is a non-essential amino acid that is primarily obtained through dietary intake. It can also be synthesized from the essential amino acid phenylalanine through a hydroxylation reaction catalyzed by the enzyme phenylalanine hydroxylase . Although this enzyme is mainly expressed in the liver, it has also been detected in melanocytes.

Melanin synthesis, including both eumelanin and pheomelanin, begins with a common biochemical pathway. In this process, the amino acid tyrosine is initially converted to L-3,4-dihydroxyphenylalanine (L-DOPA) through the action of the enzyme tyrosine hydroxylase, which utilizes tetrahydrobiopterin as a cofactor. Subsequently, tyrosinase catalyzes the oxidation of L-DOPA to dopaquinone, a crucial intermediate in melanogenesis. From this stage, the pathway diverges toward the production of either eumelanin, which appears as a brown-black pigment, or pheomelanin, characterized by red-yellow coloration, depending on the cellular conditions and the availability of substrates.

An ablative fractional laser such as the 2940-nm erbium laser produces multiple microscopic beams that create microthermal zones within the skin. These micro-injuries induce controlled thermal damage that can lead to contraction of lesional tissue and stimulate the release of cytokines and growth factors, which promote melanocyte proliferation and migration. In addition, the temporary disruption of the skin barrier enhances the penetration of topical medications and ultraviolet light, thereby improving the therapeutic response.