title: Altered platelet plug formation in hyperthyroidism and hypothyroidism.
abstract: OBJECTIVE
  Patients with thyroid diseases have abnormalities of blood coagulation including an alteration of von Willebrand factor (vWF) levels. Because vWF plays an important role in primary hemostasis, we hypothesized that heightened and decreased vWF levels in hyper- and hypothyroidism enhance and decrease platelet plug formation, respectively.
  
  
  METHODS
  We followed a cohort of 120 patients with overt hyperthyroidism, patients with subclinical and overt hypothyroidism, and euthyroid controls. vWF and in vitro platelet plug formation as collagen-epinephrine-induced closure time (CEPI-CT) were measured at baseline and during therapy with thiamazole or T(4).
  
  
  RESULTS
  Baseline vWF levels were higher in patients with hyperthyroidism and lower in patients with overt hypothyroidism than in controls (P < 0.01). High vWF antigen levels were associated with increased baseline platelet plug formation in patients with hyperthyroidism as compared with controls [114 sec (95% confidence interval, 105-122 sec) vs. 130 sec (120-140 sec), P = 0.01]. After 8 wk of therapy with thiamazole, serum concentrations of T(4) and vWF levels decreased to normal values (P < 0.01 vs. baseline), and CEPI-CT was prolonged as compared with baseline (P < 0.01). During therapy with T(4), vWF levels increased (P < 0.05 vs. baseline) and CEPI-CT was shortened as compared with baseline (P < 0.01).
  
  
  CONCLUSIONS
  Hyperthyroidism-induced vWF elevation is associated with enhanced platelet function and therefore shortened CEPI-CT values. These changes may contribute to the higher risk for cardiovascular disease in patients with hyperthyroidism. Platelet plug formation decreases during therapy with thiamazole. Furthermore, CEPI-CT appears to be sensitive to detect acquired von Willebrand disease associated with overt hypothyroidism.
authors.affiliation: Department of Internal Medicine IV, Medical University of Vienna, Austria.
authors.forename: Monika
authors.initials: M
authors.lastname: Homoncik
authors.forename: Alois
authors.initials: A
authors.lastname: Gessl
authors.forename: Arnulf
authors.initials: A
authors.lastname: Ferlitsch
authors.forename: Bernd
authors.initials: B
authors.lastname: Jilma
authors.forename: Heinrich
authors.initials: H
authors.lastname: Vierhapper
mesh_terms: D000328:Adult; D013956:Antithyroid Agents / Q000627:therapeutic use; D015331:Cohort Studies; D003094:Collagen; D004837:Epinephrine; D005169:Factor VIII / Q000378:metabolism; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000188:drug therapy; D007037:Hypothyroidism / Q000097:blood* / Q000188:drug therapy; D008297:Male; D008713:Methimazole / Q000627:therapeutic use; D008875:Middle Aged; D015999:Multivariate Analysis; D010974:Platelet Aggregation / Q000502:physiology*; D010979:Platelet Function Tests; D012310:Ristocetin / Q000378:metabolism; D013974:Thyroxine / Q000627:therapeutic use; D014662:Vasoconstrictor Agents; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D013956:Antithyroid Agents; D014662:Vasoconstrictor Agents; D014841:von Willebrand Factor; D012310:Ristocetin; D008713:Methimazole; D005169:Factor VIII; D003094:Collagen; D013974:Thyroxine; D004837:Epinephrine