Systemic mastocytosis: A cohort study on clinical characteristics of 136 patients in a large tertiary centre

• Systemic mastocytosis has a heterogeneous presentation.
• A diagnostic delay is often present.
• A normal serum tryptase cannot exclude systemic mastocytosis.
• Patients without skin involvement have a higher risk of anaphylaxis.
• Anaphylaxis and unexplained osteoporosis should trigger analysis for SM.

BackgroundSystemic mastocytosis (SM) is a rare heterogeneous disease which is characterized by the aberrant proliferation of mast cells. It can be divided into various subtypes with different phenotypes and prognoses. Here, we report on the clinical characteristics of 136 SM patients.MethodsA retrospective cohort study was conducted from January 2009 to September 2014 in a large tertiary centre in The Netherlands. We included all patients who fulfilled WHO criteria for SM. Data were collected from electronic patient files.ResultsA total of 124 patients had indolent SM (ISM) (91.2%), 7 had aggressive SM (ASM) (5.1%) and 5 had SM with associated hematological non-mast cell lineage disease (SM-AHNMD) (3.7%). There was no progression from ISM to advanced SM subtypes, but 1 patient with ASM developed chronic myelocytic leukemia 2 years after diagnosis. The average time to diagnosis for the whole population was 8.1 years (range, 0–49 years). The most frequent triggers for work-up—skin involvement, anaphylaxis and osteoporosis—were characterized by an interval to diagnosis of 10.9, 2.9 and 7.5 years, respectively. A total of 32 patients (23.5%) had a serum tryptase levels below the cutoff value of 20 ng/mL at the time of diagnosis, but these patients did not have significant differences in clinical phenotype.ConclusionsSM comprises a wide spectrum of signs and symptoms and its often atypical presentation can delay the establishment of the diagnosis substantially. Skin involvement, anaphylaxis and unexplained osteoporosis should trigger analysis for mastocytosis. A normal serum tryptase does not exclude the diagnosis of SM.