Systemic mastocytosis: A form of mastocytosis characterized by infiltrates of mast cells in the skin, lymph nodes, liver, spleen, gastrointestinal tract, bones, and joints with a predisposition to peptic ulcer due to excess stomach acid (caused by the release of histamine from the mast cells).

Treatment may include antihistamines, drugs to reduce stomach acid, migraine headache drugs for headache, and cromolyn for bowel symptoms.