Information on the following diseases can be found in the Related Disorders section of this report:

• Mastocytosis
• Papular Urticaria

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.
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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.
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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.
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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.)
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Diagnosis
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
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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The National Institute of Allergy and Infectious Diseases (NIAID) is presently (March 2003) recruiting patients with pediatric-onset mastocytosis for participation in two clinical trials. These are:

Study 1
The study of the Regulation of the Proliferation and Survival of Normal and Neoplastic Human Mast Cells seeks to enroll about 100 patients up to 80 years of age. This study, which will require the presence of participants for 1 day (eight hours) in Bethesda, Maryland, is designed to examine the growth factors that promote and/or inhibit mast cell proliferation.

Patients will be expected to volunteer for blood and bone marrow testing.

Study ID Numbers are: 020277; 02-I-0277

For further information, contact
National Institute of Allergy and Infectious Diseases
9000 Rockville Pike
Bethesda, MD 20892

Attention: Linda M. Scott, CRNP
Tel: 301-496-3915
e-mail: lmscott@niaid.nih.gov

Study 2
NIAID seeks to recruit about 30 persons up to the age of 21 who present with clear evidence of severe disease for a study of the cause and natural course of pediatric-onset mastocytosis. Blood and bone studies will be undertaken.

Study ID Numbers are: 030041; 03-I-0041

For further information, contact
National Institute of Allergy and Infectious Diseases
9000 Rockville Pike
Bethesda, MD 20892

Attention: Patient recruitment and Public Liaison Office
Tel: 1-800-411-1222
e-mail: prpl@mail.cc.nih.gov

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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McKusick VA, Ed. ONLINE MENDELIAN INHERITANCE IN MAN (OMIM). The Johns Hopkins University. Entry Number; 154800: Last Edit Date; 12/6/1999.

TEXTBOOKS
Akin C. Metcalfe DD. Mastocytosis. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:402.

Berkow R., ed. The Merck Manual-Home Edition. Whitehouse Station, NJ: Merck Research Laboratories; 1997:831.

Champion RH, Burton JL, Ebling FJG. Eds. Textbook of Dermatology. 5th ed. Blackwell Scientific Publications. London, UK; 1992:2067-71.

REVIEW ARTICLES
Escribano L, Akin C, Castells M, et al. Mastocytosis: current concepts in diagnosis and treatment. Ann Hematol. 2002;81:677-90.

Gupta R, Bain BJ, Knight CL. Cytogenic and molecular genetic abnormalities in systemic mastocytosis. Acta Haematol. 2002;107:123-28.

Valent P, Horny HP, Escribano L, et al. Diagnostic criteria and classification of mastocytosis: a consensus proposal. Leuk Res. 2001;25:603-25.

Marone G, Spadaro G, Granata F, et al. Treatment of mastocytosis: pharmacologic basis and current concepts. Leuk Res. 2001;25:583-94.

Li CY. Diagnosis of mastocytosis: value of cytochemistry and immunohistochemistry. Leuk Res. 2001;25:537-41.

Wolff K, Komar M, Petzelbauer P. Clinical and histopathological aspects of cutaneous mastocytosis. Leuk Res. 2001;25:519-28.

Bedlow AJ, Gharrie S, Harland CC. The treatment of urticaria pigmentosa with frequency-doubled Q-switch Nd:YAG laser. J Cutan Laser Ther. 2000;2:45-47.

FROM THE INTERNET
Lehrer M. Urticaria pigmentosa. MEDLINEplus. Medical Encyclopedia. Update Date 8/7/2001. 3pp.
www.nlm.nih.gov/medlineplus/ency/article/001466.htm

Mastocytosis. NIAID Fact Sheet. January 2002. 3pp.
www.niaid.nih.gov/factsheets/masto.htm

Soignee M. Urticaria Pigmentosa. nd. 2pp.
www.skinsite.com/info_urticaria_pigmentosa.htm

Akin C. Mastocytosis in Children – The Basics for Parents. Mastocytosis Pediatric Information and Parent Support. Various dates, various lengths.
http://mastokids.org/index.php?x=articles/parentsbasics.php
Diagnosis and Treatment of Mastocytosis.
http://mastokids.org/index.php?x=diagnosis.php

What are mast cells? [Etc.]
http://mastokids.org/index.php?x=articles/pedmasto.php

Urticaria pigmentosa (mastocytosis) – Information for Parents. nd. 3pp.
www.dermnetnz.org.dna.urtp/urtp.html

Lehrer M. Urticaria Pigmentosa Information. Review Date: 8/7/2001. Various lengths.
www.1uphealth.com/health/urticaria_pigmentosa.html
www.1uphealth.com/health/urticaria_pigmentosa_prognosis.html
www.1uphealth.com/health/urticaria_pigmentosa_treatment.html
www.1uphealth.com/health/urticaria_pigmentosa_diagnosis_tests.html
www.1uphealth.com/health/urticaria_pigmentosa_symptoms.html
www.1uphealth.com/health/urticaria_pigmentosa_info.html

Urticaria pigmentosa. ENLmedical. Medical Encyclopedia. nd. 5pp.
www.enlmedical.com/article/001466.htm