In patients with systemic mastocytosis, the mast cells (cells involved in allergic reactions) are present in excess numbers. Mastocytosis can be present only in the skin (cutaneous mastocytosis or chronic urticaria), but in systemic mastocytosis increased numbers of mast cells are present throughout the body, including the gastrointestinal tract and the bone marrow. Symptoms of systemic mastocytosis include allergic skin reactions, difficulty concentrating, and diarrhea.
Physicians diagnose systemic mastocytosis when they find, through biopsy, mast cells in parts of the body of other than the skin. Systemic mastocytosis is generally treated with antihistamines, but systemic mastocytosis can also be treated with chemotherapy.