Urticaria pigmentosa is a disease that produces skin lesions and intense itching. If the lesions are rubbed, hives may form on the site. Urticaria pigmentosa is the name given to a type of mastocytosis, in which there are brown patches on the skin due to abnormal collections of mast cells. Urticaria pigmentosa is characterized by several to many brownish spots that itch and, when scratched, produce welts and reddened skin. The brown spots, seen here on the chest, contain mast cells with
high levels of histamine. People sometimes develop generalized flushing and headaches from the massive histamine release from these spots.
Urticaria pigmentosa is one of several forms of mastocytosis, which is caused by excessive numbers of inflammatory cells (mast cells) in the skin. Other forms include solitary mastocytoma (a single lesion) and systemic mastocytosis (involvement in organs other than the skin). Mast cells are normally widely distributed over the skin. They contain granules that contain histamine and other chemicals. When the mast cell is disturbed, these chemicals are released into the surrounding skin. The chemicals make the blood vessels leaky, resulting in localised itching, swelling and redness.
Urticaria pigmentosa is most often seen in children, but it can occur in adults as well. Rubbing of a lesion produces a rapid wheal (a hive-like bump). Younger children may develop a fluid-filled blister over a lesion if it is scratched. A large histamine release from these extra mast cells may cause flushing, headache, diarrhea, a rapid heartbeat (tachycardia), and even fainting. This is uncommon with urticaria pigmentosa but may be seen in other forms of mastocytosis. Urticaria pigmentosa most often affects infants, with the first patches appearing at a few months of age. They are often confused with insect bites at first, but persist and gradually increase in number for several months or years. They can appear on any part of the body including the scalp, face, trunk and limbs.
In urticaria pigmentosa, one can demonstrate the presence of mast cells by rubbing one of the brown patches. Within a few minutes, the rubbed area becomes reddened, swollen and itchy. This is known as Dariers sign, and confirms the presence of mastocytosis. In young children, it is common for the patches to blister when rubbed. If many patches are activated at the same time the infant may become irritable but is uncommon for severe symptoms to arise. Over the next few years the urticaria pigmentosa becomes less irritable and eventually the patches fade away. By the teenage years, most patches will have gone. Sometimes urticaria pigmentosa develops for the first time in an adult. Few or many lesions appear and can be unsightly as well as itchy. Unfortunately, in adults urticaria pigmentosa tends to persist long term. It is also more likely to be associated with internal symptoms.
Mast cells can accumulate in other organs as well as the skin (systemic mastocytosis). If this occurs, it may cause fever, weight loss, diarrhoea and abdominal pain. Rarely, systemic mastocytosis is due to malignancy and results in a form of leukaemia. Affected sites may be bone, liver, spleen, lymph nodes or the gastrointestinal tract. Telangiectasia eruptiva macularis perstans (TEMP) is a rare form of mastocytosis in which diffuse red patches occur associated with overlying telangiectasia (dilated capillaries).
There is no satisfactory treatment for urticaria pigmentosa. Patients with urticaria pigmentosa should avoid aspirin, codeine, opiates, procaine, alcohol. polymyxin B, hot baths, and vigorous rubbing after bathing and showering. These can release histamine which can cause itching, flushing and hives. Antihistamines such as Benadryl can help control itching, hives, and flushing. Antihistamines may relieve some of the histamine-induced symptoms such as itching and flushing. Discuss the choice of antihistamine with your child's health care provider. With more severe and unusual forms of urticaria pigmentosa, systemic symptoms may need to be controlled with other medications.