Mastocytosis : Classification

Comments:
Mastocytosis is subdivided into two main categories and several subtypes based on the sites/organs involved, the extent of involvement, and clinical and laboratory findings.

Cutaneous mastocytosis (80% of cases): The abnormal mast cell infiltrates are limited to the skin and the criteria for systemic mastocytosis are absent. The most common form of cutaneous mastocytosis is maculopapular cutaneous mastocytosis (aka urticaria pigmentosa; 80% of cases) which presents most frequently in children. Solitary cutaneous mastocytoma accounts for 10-20% of cases and is seen almost exclusively in children. Diffuse cutaneous mastocytosis is extremely rare and also affects mainly children.

Systemic Mastocytosis (20% of cases): There is involvement of at least one extracutaneous organ (usually bone marrow). Cutaneous lesions are seen in about 50% of cases. The most common forms of systemic mastocytosis are indolent, but rare aggressive variants such as mast cell leukemia do occur.