Urticaria pigmentosa

What is urticaria pigmentosa?

Our immune system contains different types of cells, including mast cells. These cells help the body heal after a wound and respond to possible allergens.

Sometimes mast cells build up in large numbers outside their usual environment, causing a condition called mastocytosis. Cutaneous mastocytosis occurs when mast cells build up in skin, hair or nails. The most common type of cutaneous mastocytosis in children is urticaria pigmentosa (UP). The condition is also called maculopapular mastocytosis.

Over half of all cases of UP first appear in children aged under two. New spots can continue to appear over the next few years.

Like most childhood cutaneous mastocytoses, urticaria pigmentosa is benign (harmless). It is limited to the skin and there is little risk of symptoms that involve other organs.

UP is not a permanent disease. About half of all cases resolve by puberty and the other half improve greatly by then.

How does urticaria pigmentosa affect the body?

Positive Darier’s sign

Urticaria pigmentosa most commonly appears as red-brown spots or bumps and can affect any part of the body. The number of spots varies from child to child, from just a few to hundreds.

These spots are commonly itchy. After vigorous rubbing, they can become red and swollen, indicating that the mast cells are activated. Your doctor might describe the redness and swelling as a positive Darier’s sign.

Besides being red and itchy, the spots associated with UP can sometimes become fluid-filled blisters. They usually do not leave a scar, but they can linger for months to years.

UP is limited to the skin in most children, but, in rare cases, it can produce other symptoms such as:

• diarrhea
  
• vomiting
• flushing
• wheezing
  
• anaphylaxis (serious allergic reactions).

If your child has any of these unusual symptoms, tell your doctor at your next visit.

What causes urticaria pigmentosa?

The cause of urticaria pigmentosa is unknown, but it is thought that genetics may play a part.

How is urticaria pigmentosa diagnosed?

Urticaria pigmentosa is easily diagnosed in clinic if a child under age two has red-brown spots and a positive Darier’s sign. When the diagnosis is more uncertain, your child’s doctor may order a skin biopsy to examine the spots.

Once UP is diagnosed, a dermatologist will monitor your child every six to 12 months.

Usually your child will not need further testing. However, your doctor may consider doing a blood test or may refer your child to a hematologist (a blood specialist) if:

• your child has many spots
• the spots look unusual
• any flare ups (redness and swelling) take longer to resolve than usual
  
• your child has severe systemic complaints, such as severe vomiting, diarrhea or wheezing.

How is urticaria pigmentosa treated?

Unfortunately, there is no cure for UP. However, most children affected by the disease improve by puberty. In the meantime, the symptoms of UP can be treated successfully with a range of approaches.

Avoiding triggers

The website Mastokids features a detailed list of possible triggers and how to monitor your child for symptoms if you cannot avoid them.

Examples of common triggers include:

• medications such as aspirin, NSAIDs (such as ibuprofen), narcotics, general anaesthetics (usually older agents that are no longer being used) and x-ray contrast dye
  
• stimuli such as stress, heat and direct sunlight.

Always tell your child’s doctor if your child has UP so they can avoid using or recommending anything that may trigger your child’s symptoms.

Medications

• Antihistamines can help relieve the itchiness and other side effects of mast cell activation, such as redness and swelling.
• Corticosteroid creams can provide itch relief.
• Cromolyn sodium (an anti-inflammatory medication given through an inhaler or by mouth) helps treat any diarrhea, vomiting or other gastrointestinal complaints.
• An EpiPen can help treat severe allergic reactions. Your child should carry one with them at all times if they have a history of anaphylaxis.

Light therapy

Light therapy (PUVA) has been used successfully in some severe cases.

Complications of urticaria pigmentosa

In a very small number of cases, mast cells can build up in the liver, spleen and bone marrow. This is such a rare occurrence in children that regular screening is not recommended. Adults with UP can sometimes develop leukemia, but this is extremely rare in children.

When to see a doctor for urticaria pigmentosa

• Go to the emergency room if your child shows any signs of a severe allergic reaction or difficulty breathing.
• See your child’s dermatologist if your child develops many more or many different types of spots or if your child has new symptoms such as vomiting or diarrhea.

Further information

For more information on urticaria pigmentosa, see Mastokids.org​, a website to support children and families living with mastocytosis.​