Epidemiology of mastocytosis in adults based on a multidisciplinary diagnostic approach.

Background: Mastocytosis is a rare disease. Some epidemiological informations are available about its cutaneous form in children but very few studies addressed the issue of its incidence and prevalence in adults. Aims: We evaluated the epidemiology of mastocytosis in the adult (≥18 years) population of the Verona province (Veneto region, Italy), based on the activity of the Multisciplinary Mastocytosis Outpatient Clinic, established in Verona in January 2006. Methods: Patients with suspected mastocytosis are referred to our Clinic from a network of Allergological, Dermatological and Rheumatological Centers in Northern Italy. We focused on all the consecutive adult patients with a confirmed diagnosis of mastocytosis resident in the Verona province. The diagnosis of Cutaneous (CM) or Systemic Mastocytosis (SM) was established according to the World Health Organization Classification. Patients with Urticaria Pigmentosa who did not perform bone marrow evaluation were defined as having Mastocytosis in the Skin (MIS). Written informed consent was obtained from all the enrolled patients. Data about the general population resident in the Verona province from 2008 to 2011 were found at the www.demo.istat.it site. Historical data about the prevalence and incidence of mastocytosis in Veneto were obtained from the Veneto Tumor Registry, Istituto Oncologico Veneto-IRCCS. Results: Seventy-four adults from a total of 293 patients in our Mastocytosis Registry were identified as living in the Verona province. They were equally distributed by gender (M/F=36/38); median age at first observation was 47.5 (range 20-80) years. The reasons for referral were Urticaria Pigmentosa (n=41), anaphylaxis after hymenoptera sting (n=27) or drugs (n=2) with basal serum tryptase >11.4 ng/mL, unexplained osteoporosis (n=2), other mediator-related symptoms (n=1) and non-MC myeloid neoplasia (n=1). The diagnosis was indolent SM (ISM) in 62 (83.8%) patients; the other cases were CM (n=6), MIS (n=4), aggressive SM (n=1) and SM associated with non-MC disease (n=1). Skin involvement was significantly more frequent in females than in males (78.9% vs 47.2%, respectively, p=.007). There was a trend for a higher median basal tryptase in males vs females (19.25 vs 15.95 ng/mL, respectively, p=.054). D816V KIT mutation was found in 56/64 tested cases (87.5%). We did not find any familial case in this adult population. After a median follow-up of 36 (range 2-112) months all patients are alive. The prevalence of mastocytosis in the Verona province adult population was 9.7 per 100,000 inhabitants, without gender differences. The incidence of new cases did not substantially change from 2008 to 2011 and was 0.93-1.34 per 100,000 inhabitants/year. For comparison, the reported prevalence and incidence in Veneto region before the establishment of our activity (2002-2005) were 0.65 per 100,000 inhabitants and 0.12 new cases per 100,000 inhabitants/year, respectively. Summary / Conclusion: Although rare, mastocytosis in adults is at least 10 times more frequent than previously reported. Due to the close collaboration with all the Allergology, Dermatology and Rheumatology units of our province, we can assume that virtually all patients with suspected mastocytosis are referred to us. However, the actual prevalence may be higher because ISM diagnosis is understimated especially when skin lesions and/or mediator symptoms are absent. A multidisciplinary diagnostic approach and a wide network of specialists are needed to improve the awareness about this disease and to define its actual epidemiology.