Vitiligo

Vitiligo is a chronic autoimmune disorder characterized by the progressive destruction of melanocytes, the pigment-producing cells located in the basal layer of the epidermis, resulting in well-defined patches of depigmented (white) skin. It affects approximately 0.5-2% of the global population, with onset most commonly between ages 10 and 30 years, and affects all races and ethnicities equally, though it is more noticeable in individuals with darker skin tones. Melanocytes originate from neural crest cells during embryonic development and migrate to the epidermis, hair follicles, eyes, and inner ear. Their primary function is to produce melanin, a pigment that protects underlying cells from ultraviolet (UV) radiation damage by absorbing UV photons and dissipating the energy as heat. Melanin is synthesized within specialized organelles called melanosomes through a series of enzymatic reactions, with tyrosinase being the rate-limiting enzyme. The melanosomes are then transferred to surrounding keratinocytes via dendritic processes, providing UV protection to the entire epidermal layer. In vitiligo, melanocytes are targeted and destroyed by the immune system through several proposed mechanisms. The autoimmune hypothesis, which has the strongest evidence, involves CD8+ cytotoxic T lymphocytes that recognize melanocyte-specific antigens (such as tyrosinase, MART-1/Melan-A, and gp100) and attack melanocytes. Circulating autoantibodies against melanocyte surface antigens have been found in up to 90% of vitiligo patients. The oxidative stress hypothesis proposes that melanocytes in vitiligo have an inherent defect in handling reactive oxygen species (ROS), leading to oxidative damage that triggers the autoimmune response. Elevated levels of hydrogen peroxide have been found in the epidermis of vitiligo patients. There is also a strong genetic predisposition, with approximately 20% of vitiligo patients having a first-degree relative with the condition. The HLA associations and multiple susceptibility genes have been identified, many of which overlap with other autoimmune diseases. Vitiligo is classified into two main types. Non-segmental (generalized) vitiligo is the most common form (85-90%), presenting as bilateral, symmetric depigmented patches that typically progress over time and may affect any body surface. Segmental vitiligo is less common (10-15%), presenting as unilateral depigmented patches within a single dermatome, with earlier onset, rapid initial progression, and then stabilization. Common sites of involvement include the face (especially periorbital and perioral areas), hands, wrists, elbows, knees, axillae, and genitalia -- areas subject to friction or trauma (Koebner phenomenon). Hair in affected areas may also become white (poliosis or leukotrichia) when melanocytes in hair follicles are affected. The Wood lamp examination (ultraviolet A light at 365 nm) is a key diagnostic tool that enhances the contrast between depigmented and normally pigmented skin, making early or subtle lesions more visible. Under Wood lamp, vitiligo appears as bright blue-white fluorescent patches due to the complete absence of melanin. This is particularly useful in fair-skinned individuals where vitiligo may be difficult to see under standard lighting. The association of vitiligo with other autoimmune conditions is clinically significant. Up to 15-25% of vitiligo patients have concurrent autoimmune thyroid disease (Hashimoto thyroiditis or Graves disease), and screening with thyroid function tests is recommended. Other associated conditions include type 1 diabetes mellitus, pernicious anemia, Addison disease, alopecia areata, and rheumatoid arthritis. For the practical nurse, care focuses on psychosocial support (vitiligo significantly impacts body image and quality of life), skin protection (depigmented skin is highly susceptible to sunburn), medication application education, and screening for associated autoimmune conditions.