A biopsy showing mastocytosis, via Wikimedia Commons
Mastocytosis, also known as Urticaria Pigmentosa is a condition caused by the accumulation of too many mast cells and the precursors of mast cells, which naturally contain histamines and heparin. Although the disease is usually confined to the skin, causing lesions which can develop into hives when scratched, it can become systemic and affect the respiratory tract, the digestive tract, and other tissues.
The disease usually affects children and often resolves itself without treatment. However, a rarer form affects adults and can develop into a serious illness.
The symptoms of mastocytosis resemble an allergy, up to and including anaphylactic shock. However, instead of being set off by outside stimuli, the symptoms often come on at random. Because of its similarly to allergies, many cases of mastocytosis are misdiagnosed, making it a zebra diagnosis. The best way to reach a definitive diagnosis is with a skin biopsy.
Mastocytosis cannot be cured, but the symptoms can be managed with medication.