title: Risk factors and clinical profile of thrombotic thrombocytopenic purpura in systemic lupus erythematosus patients. Is this a distinctive clinical entity in the thrombotic microangiopathy spectrum?: a case control study.
abstract: BACKGROUND
  The association of thrombotic thrombocytopenic purpura (TTP) with systemic lupus erythematosus (SLE) is rare. It is associated with high morbidity and mortality. Information about risk factors and clinical outcomes is scant.
  
  
  METHODS
  A retrospective case-control study was performed in a referral center in Mexico City between 1994 and 2013. Patients were diagnosed with TTP if they fulfilled the following criteria: microangiopathic haemolytic anaemia, thrombocytopenia, high LDH levels, normal fibrinogen and negative Coombs' test. Patients with SLE were diagnosed with ≥ 4 ACR criteria. We included three study groups: group A included patients with SLE-associated TTP (TTP/SLE; cases n = 22, TTP events n = 24); patients with non-autoimmune TTP (NA-TTP; cases n = 19, TTP events n = 22) were included in group B and patients with SLE without TTP (n = 48) in group C.
  
  
  RESULTS
  After multivariate analysis, lymphopenia < 1000/mm3 [OR 19.84, p = 0.037], high SLEDAI score three months prior to hospitalisation [OR 1.54, p = 0.028], Hg <7g/dL [OR 6.81, p = 0.026], low levels of indirect bilirubin [OR 0.51, p = 0.007], and less severe thrombocytopenia [OR 0.98, p = 0.009] were associated with TTP in SLE patients. Patients with TTP/SLE received increased cumulative steroid dose vs. NA-TTP (p = 0.006) and a higher number of immunosuppressive drugs (p = 0.015). Patients with TTP/SLE had higher survival than NA-TTP (p=0.033); however, patients hospitalised for TTP/SLE had a higher risk of death than lupus patients hospitalised for other causes
  
  
  CONCLUSIONS
  Lymphopenia is an independent risk factor for TTP/SLE. It is likely that patients with TTP/SLE present with less evident clinical features, so the level of suspicion must be higher to avoid delay in treatment.
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: oyarem@hotmail.com.
authors.forename: Javier
authors.initials: J
authors.lastname: Merayo-Chalico
authors.affiliation: Department of Haematology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Mexico City, Mexico. Electronic address: r_demichelis@hotmail.com.
authors.forename: Roberta
authors.initials: R
authors.lastname: Demichelis-Gómez
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: srajme@hotmail.com.
authors.forename: Sandra
authors.initials: S
authors.lastname: Rajme-López
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: alberto_aparicio@live.com.mx.
authors.forename: Luis
authors.initials: L
authors.lastname: Aparicio-Vera
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: anabar9@hotmail.com.
authors.forename: Ana
authors.initials: A
authors.lastname: Barrera-Vargas
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: jorgealcocer2@gmail.com.
authors.forename: Jorge
authors.initials: J
authors.lastname: Alcocer-Varela
authors.affiliation: Department of Immunology and Rheumatology, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Vasco de Quiroga 15, Tlalpan 14000, Mexico City, Mexico. Electronic address: d_gomar@hotmail.com.
authors.forename: Diana
authors.initials: D
authors.lastname: Gómez-Martín
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000150:complications* / Q000628:therapy; D008231:Lymphopenia / Q000150:complications; D008297:Male; D008800:Mexico / Q000453:epidemiology; D011697:Purpura, Thrombotic Thrombocytopenic / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D012189:Retrospective Studies; D012307:Risk Factors; D016019:Survival Analysis
keywords: Lymphopenia; Systemic lupus erythematosus; Thrombotic thrombocytopenic purpura