Urticaria pigmentosa

Urticaria pigmentosa is the most common form of cutaneous mastocytosis. It is a rare disease caused by excessive amounts of mast cells in the skin that produce hives or lesions on the skin when irritated.

Prevalence
Urticaria pigmentosa is an orphan disease, affecting fewer than 200000 people in the United States.

Diagnosis
The disease is most often diagnosed as an infant, when parents take their baby in for what appears to be bug bites. The bug bites are actually the clumps of mast cells. Doctors can confirm the presence of mast cells by rubbing the baby's skin. If hives appear, it most likely signifies the presence of urticaria pigmentosa.

Symptoms
Urticaria Pigmentosa is characterized by excessive amounts of mast cells in the skin. Red or brown spots are often seen on the skin, typically around the chest and forehead. These mast cells, when irritated (e.g. by rubbing the skin, heat exposure), produce too much histamine, triggering an allergic reaction that leads to hives localized to the area of irritation, sometimes referred to as Darier's sign. Severe itching usually follows, and scratching the area only serves to further symptoms. Symptoms can range from very mild (flushing, hives, no treatment needed) to life-threatening (vascular collapse).

Irritants
The following can worsen the symptoms of urticaria pigmentosa:


 * 1) Emotional stress
 * 2) Physical stimuli such as heat, friction, and excessive exercise
 * 3) Bacterial toxins
 * 4) Venom
 * 5) Eye drops containing dextran
 * 6) NSAIDs
 * 7) Alcohol
 * 8) Morphine

The classification of NSAIDs can be disputed. Aspirin, for example, causes the mast cells to degranulate, releasing histamines and causing symptoms to flare. However, daily intake of 81mg aspirin may keep the mast cells degranulated. Thus, while symptoms may be worsened at first, they can get better as the mast cells are unable to recover.

Treatments
There are no cures for urticaria pigmentosa. However, treatments are possible. Most treatments for mastocytosis can be used to treat urticaria pigmentosa.

At least one clinical study suggested that nifedipine, a calcium channel blocker used to treat high blood pressure, may reduce mast cell degranulation in patients with urticaria pigmentosa. A 1984 study by Fairly et al. included a patient with symptomatic urticaria pigmentosa who responded to nifedipine at dose of 10 mg po tid. However, nifedipine has never been approved by the FDA for treatment of urticaria pigmentosa.