Diagnostic criteria and classification of mastocytosis: a consensus proposal

The term 'mastocytosis' denotes a heterogeneous group of disorders characte rized by abnormal growth and accumulation of mast cells (MC) in one or more organ systems. Over the last 20 years, there has been an evolution in acce pted classification systems for this disease. In light of such developments and novel useful markers, it seems appropriate now to re-evaluate and upda te the classification of mastocytosis. Here, we propose criteria to delinea te categories of mastocytosis together with an updated consensus classifica tion system. In this proposal, the diagnosis cutaneous mastocytosis (CM) is based on typical clinical and histological skin lesions and absence of def initive signs (criteria) of systemic involvement. Most patients with CM are children and present with maculopapular cutaneous mastocytosis (= urticari a pigmentosa, UP). Other less frequent forms of CM are diffuse cutaneous ma stocytosis (DCM) and mastocytoma of skin. Systemic mastocytosis (SM) is com monly seen in adults and defined by multifocal histological lesions in the bone marrow (affected almost invariably) or other extracutaneous organs (ma jor criteria) together with cytological and biochemical signs (minor criter ia) of systemic disease (SM-criteria). SM is further divided into the follo wing categories: indolent systemic mastocytosis (ISM), SM with an associate d clonal hematologic non-mast cell lineage disease (AKNMD), aggressive syst emic mastocytosis (ASM), and mast cell leukemia (MCL). Patients with ISM us ually have maculopapular skin lesions and a good prognosis. In the group wi th associated hematologic disease, the AHNMD should be classified according to FAB/WHO criteria. ASM is characterized by impaired organ-function due t o infiltration of the bone marrow, liver, spleen, GI-tract, or skeletal sys tem, by pathologic MC. MCL is a 'high-grade' leukemic disease defined by in creased numbers of MC in bone marrow smears (greater than or equal to 20%) and peripheral blood, absence of skin lesions, multiorgan failure, and a sh ort survival. In typical cases, circulating MC amount to greater than or eq ual to 10% of leukocytes (classical form of MCL). Mast cell sarcoma is a un ifocal tumor that consists of atypical MC and shows a destructive growth wi thout (primary) systemic involvement. This high-grade malignant MC disease has to be distinguished from a localized benign mastocytoma in either extra cutaneous organs (= extracutaneous mastocytoma) or skin. Depending on the c linical course of mastocytosis and development of an AHNMD, patients can sh ift from one category of MC disease into another. In all categories, mediat or-related symptoms may occur and may represent a serious clinical problem. All categories of mastocytosis should be distinctively separated from reac tive MC hyperplasia, MC activation syndromes, and a more or less pronounced increase in MC in myelogenous malignancies other than mastocytosis. Criter ia proposed in this article should be helpful in this regard. (C) 2001 Else vier Science Ltd. All rights reserved.