title: The clinical relevance of the IgM isotype of antiphospholipid antibodies in the vascular antiphospholipid syndrome.
abstract: OBJECTIVE
  Because it has been suggested that the IgM isotype of antiphospholipid (aPL) antibodies should no longer be included in the laboratory criteria for antiphospholipid syndrome (APS) classification, we assess the clinical relevance of IgM isotype of aPL in a cohort of patients with vascular APS.
  
  
  METHODS
  Mean age, sex, the presence of autoimmune diseases other than systemic lupus erythematosus, risk factors for thrombosis, the type/s and site/s of thromboembolic events, the levels of C3 and C4, and autoantibody profile were evaluated in a large cohort of persistently aPL positive patients fulfilling the Sydney criteria for APS. Patients with isolated IgM isotype were compared for each variable with those with any other aPL antibody combination.
  
  
  RESULTS
  One hundred six patients were assessed; of these 55 (51.9%) had venous thromboembolism, 48 (45.3%) arterial thrombosis, and 3 (2.8%) small vessel thrombosis. Positivity to only IgM aPL made possible to classify 13 patients (12.3%) as vascular APS. In all cases the presence of IgM aPL was at medium-high titer, confirmed, and found to be stable in the time. There were four patients with retinal thrombosis (3.8%) and the prevalence of this event was significant in the isolated IgM isotype positive patients (p=0.005).
  
  
  CONCLUSIONS
  Data from this investigation give clinical value to the IgM isotype of aPL and suggest to consider aCL and anti-β2GPI of IgM class as valid laboratory criteria for APS classification, especially when they are associated and stable overtime.
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy. Electronic address: teresa.delross@sanita.padova.it.
authors.forename: Teresa
authors.initials: T
authors.lastname: Del Ross
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Amelia
authors.initials: A
authors.lastname: Ruffatti
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Cuffaro
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Tonello
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Antonia
authors.initials: A
authors.lastname: Calligaro
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Favaro
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Myriam
authors.initials: M
authors.lastname: Facchinetti
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Ariela
authors.initials: A
authors.lastname: Hoxha
authors.affiliation: Rheumatology Unit, Department of Medicine - DIMED, Via Giustiniani 2, 35128, University of Padua, Padua, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Punzi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017152:Antibodies, Antiphospholipid / Q000276:immunology*; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D002648:Child; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D017152:Antibodies, Antiphospholipid; D007075:Immunoglobulin M
keywords: Antiphosholipid antibody syndrome; Classification criteria; IgM isotype; Retinal thrombosis; Thrombosis