2. What is Mastocytosis ?
Mastocytosis is a disease that is characterized by abnormal growth and accumulation of mast cells in i) the skin, ii) in internal organs, or iii) in both skin and internal organs.
As a result, mastocytosis is a disorder with presence of too many mast cells (extra mast cells) in a person's body. Both children and adults can develop mastocytosis.
Traditionally, mastocytosis is classified as being either cutaneous mastocytosis (CM) or systemic mastocytosis (SM). In cutaneous mastocytosis, mast cell accumulation is only found in the skin.
To diagnose CM, a biopsy of affected skin has to be performed. The pure cutaneous form of mastocytosis is usually diagnosed in (early) childhood. By contrast, most patients in adulthood are diagnosed to have systemic mastocytosis. Most of the adult patients have typical skin lesions commonly termed urticaria pigmentosa. Since the bone marrow is almost always involved in these patients (but not in those with CM), the diagnosis of systemic mastocytosis in adults is usually established by a biopsy of the bone marrow. In the rare patients without skin lesions, it may take a longer time until the doctors consider a systemic mast cell disease as a diagnosis, and thus it may take a longer time until the final diagnosis SM can be established.
Systemic mastocytosis (SM) is a disease that arises on the basis of i. enhanced development of mast cells from their progenitor cells in one or more organs and (plus) ii. enhanced accumulation of these mast cells in the respective tissue(s). In contrast to a reactive mast cell hyperplasia (increase in mast cells during an inflammation, cancer, or fibrosis), mast cells in systemic mastocytosis (SM) are monoclonal in nature, i.e. derived from a single abnormal (= neoplastic) cell (clone). In cutaneous pediatric mastocytosis, the nature of mast cell-accumulation has not yet been entirely clarified. In some of these patients, mast cells also appear to be monoclonal in nature.
Monoclonality of mast cells in mastocytosis can be documented best by demonstrating the presence of a point mutation in the c-kit proto-oncogene. In the majority of all patients with systemic mastocytosis, the somatic c-kit mutation D816V (Asp-816-Val) is detected in the bone marrow, and often also in lesional skin (where mast cells reside in macules). In a smaller group of patients with systemic mastocytosis, the mutation can also be found in circulating (peripheral) white blood cells. By contrast, in cutaneous mastocytosis, the c-kit mutation D816V is usually not detectable in any organ. |
