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Urticaria pigmentosa is a rare skin disorder that is a localized (cutaneous) form of mastocytosis. Some clinicians suggest that urticaria pigmentosa is the childhood form of mastocytosis. Mast cells are specialized cells of connective tissue that release substances such as histamine (a chemical important in the inflammatory process) and heparin (an anti-clotting agent) when the body's alarm mechanism is set off. When mast cells cluster and multiply excessively (proliferate), histamine and heparin are released into the skin (mastocytosis). The characteristic skin lesions of urticaria pigmentosa appear in these areas. Urticaria pigmentosa is generally benign and is usually self-limited. The exact cause of the disease is not known, although some cases may be inherited.
The symptoms of urticaria pigmentosa include the appearance of reddish-brown itchy spots that look like freckles (pruritic macules) and/or bumps (papules) that appear on the skin. In rare cases, lesions may also develop in bones and/or other organs of the body. When skin lesions are touched and/or exposed to heat, they become smooth, slightly elevated, and redder or paler than the surrounding skin (urticarial). This reaction is known as Darier's sign. These areas, which are called wheals or more commonly hives, are usually extremely itchy and may change in size and shape within hours. Sometimes these wheals may resemble fluid-filled blisters (bullous).
Other uncommon symptoms of urticaria pigmentosa may include headache, a general feeling of ill health (malaise), flushing, abdominal pain, diarrhea, and/or an elevated heart rate (tachycardia). These symptoms are more characteristic of systemic mastocytosis. (For more information on mastocytosis, see the Related Disorders section of this report.)
In most cases, the symptoms of urticaria pigmentosa last for a few years and then resolve. Some individuals may have areas of lightly pigmented skin that remain for many years.
The exact cause of urticaria pigmentosa is not fully understood. Some cases occur for no apparent reason (sporadically), while others are thought to be inherited as an autosomal dominant genetic trait. However, not all children with the defective gene for urticaria pigmentosa will exhibit all of the characteristics of the gene (reduced penetrance).
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Urticaria pigmentosa is a rare disorder that affects males and females in equal numbers. The symptoms typically begin during the first year of life. Skin lesions generally disappear by adolescence. Urticaria pigmentosa occurs more frequently in children who also have allergies such as hay fever and/or asthma. Approximately 50 cases of the inherited form of urticaria pigmentosa have been reported in the medical literature.
Symptoms of the following disorders can be similar to those of urticaria pigmentosa. Comparisons may be useful for a differential diagnosis:
Mastocytosis is an inherited blood disorder characterized by the presence of abnormal numbers of mast cells in the skin, bone, bone marrow, lungs, liver, spleen, and/or membranes that line the brain (meninges). When the disease is localized to the skin in children, it is known as urticaria pigmentosa. In adults, symptoms may include a vague sense of ill health, weight loss, diarrhea, nausea, vomiting, and/or an irregular heart beat. The spleen, liver, and/or numerous lymph nodes may become swollen. (For more information on this disorder, choose "Mastocytosis" as your search term in the Rare Disease Database.)
Papular urticaria, more commonly known as hives, is characterized by local elevated ridges (wheals) and redness (erythema) of the skin. This condition is usually triggered by allergic reactions to insect bites, sensitivity to drugs, or other environmental causes. The first symptom of papular urticaria is usually itching (pruritus), followed shortly by the appearance of wheals that may remain small or become large. The larger wheals tend to be clear in the center, and may be noticed first as large rings of erythema and swelling (edema). Ordinarily, crops of hives come and go. A lesion may remain for several hours, then disappear only to reappear elsewhere. (For more information on this disorder, choose "Papular Urticaria" as your search term in the Rare Disease Database.)
The diagnosis of Urticaria pigmentosa is confirmed by a clinical evaluation and the microscopic examination of skin tissue samples. In some cases, laboratory testing may reveal elevated levels of histamine and a particular enzyme (mast cell tryptase protein) in the blood of affected individuals. Affected patients exhibit persistent, rather than transitory, levels of blood histamine and tryptase.
Treatment of urticaria pigmentosa is symptomatic and supportive. Steroid creams applied to the skin (topical steroids) may be useful for some children with this disease. Antihistamine drugs may also be given by mouth to help relieve itching.
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People with urticaria pigmentosa have been treated experimentally with oral disodium cromoglycate, cimetidine (an H-2 antihistamine), or cimetidine/ketotifen combined with chlorpheniramine or propantheline. More study is needed to determine the long-term safety and effectiveness of these drugs and the various drug combinations for the treatment of urticaria pigmentosa.
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Report last updated: 2008/03/18 00:00:00 GMT+0