Page 349 - Essential Haematology

Chapter 25 Bleeding disorders / 335

ciency virus (HIV) infection or Helicobacter pylori , Clinical f eatures

chronic lymphocytic leukaemia (CLL), Hodgkin The onset is often insidious with petechial haemor-
lymphoma or autoimmune haemolytic anaemia rhage, easy bruising and, in women, menorrhagia.
(Table 25.2 ). Mucosal bleeding (e.g. epistaxes or gum bleeding)
occurs in severe cases but fortunately intracranial

Pathogenesis haemorrhage is rare. The severity of bleeding in ITP
Platelet autoantibodies (usually IgG) result in the is usually less than that seen in patients with com-
premature removal of platelets from the circulation parable degrees of thrombocytopenia from bone
by macrophages of the reticuloendothelial system, marrow failure; this is attributed to the circulation
especially the spleen (Fig. 25.4 ). In many cases, the of predominantly young, functionally superior
antibody is directed against antigen sites on the platelets in ITP. Chronic ITP tends to relapse and
glycoprotein (GP) IIb – IIIa or Ib complex. Th e remit spontaneously so the course may be diffi cult
normal lifespan of a platelet is 7 – 10 days but in ITP to predict. Many asymptomatic cases are discovered
this is reduced to a few hours. Total megakaryocyte by a routine blood count.

mass and platelet turnover are increased in parallel The spleen is not palpable unless there is an
to approximately five times normal. associated disease causing splenomegaly.

TPO-RA pathway TPO pathway
Bone marrow

TPO- TPO- Liver
RA RA TPO TPO
Megakaryocyte
Bloodstream Bloodstream
Protoplatelets
Platelets
Platelets

B lymphocyte

Antibodies

Figure 25.4 The pathogenesis of

thrombocytopenia in autoimmune
thrombocytopenic purpura. The actions
of thrombopoietin (TPO) and thrombo-
poietin receptor agonists (TPO - RA)
(thrombomimetics) are shown. These are
orally active or given by injection. They
increase platelet production. Platelets Macrophage
coated by antibodies are phagocytosed
Platelet phagocytosis
by macrophages.