Medical Definition of mastocytosis
: excessive proliferation of mast cells in the tissues; specifically : a rare variable disorder marked by the abnormal proliferation and accumulation of mast cells in the skin, bone marrow, or internal organs ◆A benign, cutaneous form of mastocytosis (see urticaria pigmentosa) occurs typically in children and may affect many areas of the skin. A less common, systemic form, usually of adults may affect multiple organs (such as the liver, spleen, and intestine), lymph nodes, and bone marrow and typically occurs as a benign, slowly progressing, indolent condition with normal life expectancy but may sometimes occur as an aggressive, often fatal condition. The most common form of mastocytosis in childhood is urticaria pigmentosa. In this disorder, mast cells accumulate in the skin, forming reddish-brown papules and plaques …—Melissa M. Burnett et al., The New England Journal of Medicine, 20 Dec. 2007 Systemic mastocytosis is characterised by diffuse mast-cell infiltration of multiple organs and may affect approximately 10% of all patients with mastocytosis.—Takashi Koide et al., The Lancet, 15 June 2002
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