OBJECTIVES: Systemic mastocytosis (SM) is a rare, clonal mast cell disease associated with the KIT D816V mutation and caused by mast cell accumulation and activation. Indolent systemic mastocytosis (ISM) represents approx. 90% of all cases of SM. SM patients are characterized by debilitating skin, gastrointestinal, neurocognitive, musculoskeletal, and systemic manifestations, including anaphylaxis. Epidemiological data are limited. This study aimed to assess the incidence and prevalence of SM and prevalence of ISM in Germany.

METHODS: A retrospective claims data analysis based on German statutory health insurance data from the InGef research database was conducted. Incidence and prevalence of adult SM patients, including advanced SM, smoldering SM and ISM patients, with at least one ICD-10-GM diagnosis code of C94.3/C96.2/D47.0 in the inpatient and/or outpatient sector in 2021 were assessed.

For the analysis of ISM prevalence for 2021, a subset of adult patients with at least two ICD‑10‑GM diagnosis codes for ISM (D47.0) in two different quarters in the inpatient and/or outpatient sector (M2Q fulfilled) were selected. To omit overlap, patients with ISM and advanced SM diagnosis code within the same year were excluded.

RESULTS: In 2021, 139 incident and 339 prevalent adult SM patients were identified, corresponding to 1-year incidence and prevalence rates of 3.93 and 9.59 per 100,000 individuals, respectively. Further, there were 164 adult ISM patients who fulfilled M2Q criteria in 2021. After exclusion of 13 patients with advanced SM, 151 adult ISM patients were identified, resulting in 1-year prevalence of ISM of 3.89 per 100,000 individuals.

CONCLUSIONS: The estimated results for SM incidence are up to 5-fold higher than in published literature. The estimated results for SM prevalence are consistent with published literature (which is also confirmed by our previous study of 2020). However, focusing the study population to ISM patients and applying additional quality criteria resulted in 2.5-fold lower prevalence.