BACKGROUND: Mastocytosis in adults often presents with skin lesions. A bone marrow biopsy is necessary to confirm or exclude the presence of systemic mastocytosis (SM) in these cases. When a bone marrow biopsy is not performed, the provisional diagnosis is mastocytosis in the skin (MIS). No generally accepted scoring system has been established to estimate the risk of SM in these patients. OBJECTIVE: To develop a risk score to predict SM in adults with MIS. METHODS: We examined 1145 patients with MIS from the European Competence Network on Mastocytosis Registry who underwent a bone marrow biopsy. A total of 944 patients had SM and 201 patients had cutaneous mastocytosis; 63.7% were female, and 36.3% were male. Median age was 44 ± 13.3 years. The median serum tryptase level amounted to 29.3 ± 81.9 ng/mL. We established a multivariate regression model using the whole population of patients as a training and validation set (bootstrapping). A risk score was developed and validated with receiver-operating curves. RESULTS: In the multivariate model, the tryptase level (P < .001), constitutional/cardiovascular symptoms (P = .014), and bone symptoms/osteoporosis (P < .001) were independent predictors of SM (P < .001; sensitivity, 90.7%; specificity, 69.1%). A 6-point risk score was established (risk, 10.7%-98.0%) and validated. CONCLUSIONS: Using a large data set of the European Competence Network on Mastocytosis Registry, we created a risk score to predict the presence of SM in patients with MIS. Although the score will need further validation in independent cohorts, our score seems to discriminate safely between patients with SM and with pure cutaneous mastocytosis.

Allergy Unit Verona University Hospital Verona Italy

Department for Hematology and Internal Oncology Kepler University Hospital Linz Austria

Department for Hematology and Internal Oncology Kepler University Hospital Linz Austria; Johannes Kepler University Linz Austria

Department of Allergology Medical University of Gdańsk Gdańsk Poland

Department of Dermatology and Allergy Biederstein School of Medicine Technical University of Munich Munich Germany

Department of Dermatology and Venereology Akademiska University Hospital Uppsala and Department of Medical Sciences Uppsala University Uppsala Sweden

Department of Dermatology and Venereology Medical University of Graz Graz Austria

Department of Dermatology and Venerology Kepler University Hospital Johannes Kepler University Linz Austria

Department of Dermatology University of Cologne Cologne Germany

Department of Dermatology University of Cologne Cologne Germany; Division of Allergy Department of Dermatology University of Basel Basel Switzerland

Department of General Internal Medicine Allergy and Clinical Immunology University Hospitals Leuven and KU Leuven Department of Microbiology Immunology and Transplantation Allergy and Clinical Immunology Research Group Leuven Belgium

Department of Hematological Biology Pitié Salpêtrière Hospital Paris Sorbonne University Paris France

Department of Hematology and Oncology University Hospital Mannheim Heidelberg University Mannheim Germany

Department of Hematology Oncology IRCCS Policlinico San Matteo Foundation Pavia Pavia Italy

Department of Hematology Oncology School of Hematology University of Pavia and IRCCS Policlinico San Matteo Foundation Pavia Italy

Department of Hematology University Medical Center Groningen University of Groningen Groningen the Netherlands

Department of Internal Medicine 1 Division of Hematology and Hemostaseology Medical University of Vienna Vienna Austria; Ludwig Boltzmann Institute for Hematology and Oncology Medical University of Vienna Vienna Austria

Department of Internal Medicine 1 Division of Hematology and Hemostaseology Medical University of Vienna Vienna Austria; Ludwig Boltzmann Institute for Hematology and Oncology Medical University of Vienna Vienna Austria; Department Hospital for Companion Animals and Horses University Clinic for Small Animals Internal Medicine Small Animals University of Veterinary Medicine Vienna Austria

Department of Internal Medicine Section of Allergy University Medical Center Groningen University of Groningen Groningen the Netherlands

Department of Medicine 1 Medical Center University of Freiburg Faculty of Medicine University of Freiburg Freiburg Germany; Department of Hematology and Oncology Medical Center University of Schleswig Holstein Campus Lübeck Lübeck Germany

Department of Medicine 1 Medical Center University of Freiburg Faculty of Medicine University of Freiburg Freiburg Germany; German Cancer Consortium Partner site Freiburg Freiburg Germany

Department of Oncology Hematology Hemostaseology and Stem Cell Transplantation Medical Faculty University Hospital RWTH Aachen Aachen Germany

Division of Allergy and Clinical Immunology Department of Medicine University of Salerno Salerno Italy

Division of Hematology Department of Internal Medicine University of Istanbul Istanbul Turkey

Faculty of Medicine and Health Sciences Department of Immunology Allergology Rheumatology University of Antwerp and Antwerp University Hospital Antwerpen Belgium

Imagine Institute Université Paris Descartes Sorbonne Paris Cité Centre national de référence des mastocytoses Paris France

Pediatric Dermatology Unit Department of Medicine University of Padua Padua Italy

Section of Hematology Department of Medicine Verona University Hospital Verona Italy

Stanford Cancer Institute Stanford University School of Medicine Stanford Calif

University Hospital Brno Brno Czech Republic

University Hospital of Leipzig Leipzig Germany

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