Vitiligo is a chronic autoimmune disorder that causes patches of skin to lose pigment or color. The cause of vitiligo is unknown, but it may be related to immune system changes, genetic factors, stress, or sun exposure. Treatment options include topical medications, light therapy, surgery and cosmetics.
Signs and symptoms
The only sign of vitiligo is the presence of pale patchy areas of depigmented skin which tend to occur on the extremities. Some people may experience itching before a new patch occurs. The patches are initially small, but often grow and change shape. When skin lesions occur, they are most prominent on the face, hands and wrists. The loss of skin pigmentation is particularly noticeable around body orifices, such as the mouth, eyes, nostrils, genitalia and umbilicus. Some lesions have increased skin pigment around the edges. Those affected by vitiligo who are stigmatized for their condition may experience depression and similar mood disorders.
Causes
Although multiple hypotheses have been suggested as potential triggers that cause vitiligo, studies strongly imply that changes in the immune system are responsible for the condition. Vitiligo has been proposed to be a multifactorial disease with genetic susceptibility and environmental factors both thought to play a role.
The National Institutes of Health states that some believe that sunburns can cause or exacerbate the condition, but this idea is not well-supported by good evidence.
Immune
Melanin is the pigment that gives skin its color; it is produced by skin cells called melanocytes.
Variations in genes that are part of the immune system or part of melanocytes have both been associated with vitiligo. It is also thought to be caused by the immune system attacking and destroying the melanocytes of the skin. A genome wide association study found approximately 36 independent susceptibility loci for generalized vitiligo.
The TYR gene encodes the protein tyrosinase, which is not a component of the immune system, but is an enzyme of the melanocyte that catalyzes melanin biosynthesis, and a major autoantigen in generalized vitiligo.
Autoimmune associations
Vitiligo is sometimes associated with autoimmune and inflammatory diseases such as Hashimoto's thyroiditis, scleroderma, rheumatoid arthritis, type 1 diabetes mellitus, psoriasis, Addison's disease, pernicious anemia, alopecia areata, systemic lupus erythematosus, and celiac disease.
Among the inflammatory products of NLRP1 are caspase 1 and caspase 7, which activate the inflammatory cytokine interleukin-1β. Interleukin-1β and interleukin-18 are expressed at high levels in people with vitiligo. In one of the mutations, the amino acid leucine in the NALP1 protein was replaced by histidine (Leu155 → His). The original protein and sequence is highly conserved in evolution, and is found in humans, chimpanzee, rhesus monkey, and the bush baby. Addison's disease (typically an autoimmune destruction of the adrenal glands) may also be seen in individuals with vitiligo.
Diagnosis
An ultraviolet light can be used in the early phase of this disease for identification and to determine the effectiveness of treatment. Using a Wood's light, skin will change colour (fluoresce) when it is affected by certain bacteria, fungi, and changes to pigmentation of the skin.
Classification
Classification attempts to quantify vitiligo have been analyzed as being somewhat inconsistent, while recent consensus have agreed to a system of segmental vitiligo (SV) and non-segmental vitiligo (NSV). NSV is the most common type of vitiligo.
Non-segmental
In non-segmental vitiligo (NSV), there is usually some form of symmetry in the location of the patches of depigmentation. New patches also appear over time and can be generalized over large portions of the body or localized to a particular area. Extreme cases of vitiligo, to the extent that little pigmented skin remains, are referred to as vitiligo universalis. NSV can come about at any age (unlike segmental vitiligo, which is far more prevalent in teenage years).
Classes of non-segmental vitiligo include the following:
Generalized vitiligo: the most common pattern, wide and randomly distributed areas of depigmentation Universal vitiligo: depigmentation encompasses most of the body Focal vitiligo: one or a few scattered macules in one area, most common in children Acrofacial vitiligo: fingers and periorificial areas Mucosal vitiligo: depigmentation of only the mucous membranes