Incidence, Diagnosis, and Outcome of Acquired Thrombotic Thrombocytopenic Purpura (aTTP): A Nationwide Survey By the Spanish Apheresis Group

Introduction: Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare disease characterized by a severe deficiency of the enzymatic activity of ADAMTS13 caused by autoantibodies, with an incidence of 3-4 x106inhabitants per year according to the few published data available. Accurate estimates of the incidence of aTTP are important to assess the resources required for current treatments and to anticipate the need to develop new treatments. The aim of this study was to determine the actualincidence of aTTP in Spain, as well as its diagnosis, management, and associated complications. Material and methods:A cross-sectional surveywascarried out among hematologists working in Spanish hospitals by means of an email that was sent to all members of the three main hematological scientificsocieties of Spain. All participants were asked to report the number of patients over the age of 16 years with a de novodiagnosis and relapses examined between Jan 2015 and Dec 2017. They were also asked about the number of patients that were known and alive in each hospital without having experienced any episode during such period. The population area of each participating hospital was consideredto calculate the incidence and prevalence of the disease. We also estimated the hospitalization service, mean hospital stay, percentage of ADAMTS13 activity at diagnosis and during follow-up, initial management, refractory cases and exacerbations (as defined by Scully et al.), treatment-related complications, and sequelae of aTTP. The median, interquartile ranges, and percentages were used for the descriptive analysis. Given that no personal data were treated, this study did not require the approval of a Research Ethics Committee. Results:A response was received from 42 centers (Figure 1). All hospitals except a private one belonged to the Spanish public health system, which provides health coverage to the entire Spanish population.A total of 203 episodes were reported (138 new episodes). The calculated population of the participating centers was nearly 21 x 106inhabitants. The incidence was 2.25 x106inhabitants per year, and the prevalence 19 x106inhabitants. Six patients died before they could start treatment (all but one in first episodes) and five were sent to other hospitals; thus, a total of 192 episodes were eventually treated. Table 1 and 2 show the data of the enzymatic activity of ADAMTS13 and the ADAMTS13 inhibitor at diagnosis, as well asthe complications. Plasma exchange