title: Seasonal association of thrombotic thrombocytopenic purpura.
abstract: BACKGROUND
  Thrombotic thrombocytopenic purpura (TTP), a thrombotic microangiopathy, is a clinical diagnosis, characterized by microangiopathic hemolytic anemia and thrombocytopenia without another likely explanation. Some initiators of the disease are well represented in the literature, such as certain drugs, malignancies, and viral illness; however, there are less objective factors still being investigated, with references to hormonal, stress, and seasonal variations considered anecdotally. A better insight of these factors would aid in understanding the pathophysiology of the disease.
  
  
  METHODS
  We performed a retrospective review of all idiopathic TTP cases treated with therapeutic plasma exchange at our institution from 1999 to 2008 to determine whether there was seasonal variation in TTP presentation. Seasons were defined as follows: winter = December to February; spring = March to May; summer = June to August; and fall = September to November. With the use of Poisson regression models, the incidence between seasons was compared.
  
  
  RESULTS
  During this study period, a total of 97 cases were recorded. Summer had the highest occurrence of TTP (35%). This was significant compared to the fall (p = 0.012) and the winter (p = 0.019). There were more cases in the summer compared to the spring, but this was not significant.
  
  
  CONCLUSIONS
  In our population, there was a significant difference in the number of TTP cases presenting in summer compared to fall and winter. This supports a possible environmental, infectious, or physiologic influence associated with the summer.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA. yapark@unch.unc.edu
authors.forename: Yara A
authors.initials: YA
authors.lastname: Park
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Poisson
authors.forename: Matthew T
authors.initials: MT
authors.lastname: McBee
authors.forename: Araba
authors.initials: A
authors.lastname: Afenyi-Annan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011697:Purpura, Thrombotic Thrombocytopenic / Q000453:epidemiology*; D012189:Retrospective Studies; D012621:Seasons