AUGUST 1, 2001 / VOLUME 64, NUMBER 3
www.aafp.org/afp
AMERICAN FAMILY PHYSICIAN
419
vessel wall and, in response to the exposed
subendothelial collagen, release adenosine
diphosphate (ADP) and thromboxane A2.3
The released ADP and thromboxane A2 cause
further platelet aggregation and the formation
of a platelet plug that is responsible for pri-
mary hemostasis.2,3
Secondary hemostatic mechanisms consist
of a series of sequential enzymatic reactions
involving various coagulation factors and
leading to the formation of a fibrin clot. The
intrinsic pathway is activated by the exposed
collagen, and the extrinsic pathway is activated
by tissue thromboplastin (Figure 1).3
The integrity of the vascular system depends
on three interacting elements: platelets, plasma
coagulation factors and blood vessels. All three
elements are required for proper hemostasis,
but the pattern of bleeding depends to some
extent on the specific defect. In general, platelet
disorders manifest petechiae, mucosal bleed-
ing (wet purpura) or, rarely, central nervous
system bleeding; coagulation disorders present
as ecchymoses or hemarthrosis; and vasculitic
disorders present with palpable purpura.1
Platelet Disorders
Simple purpura strongly indicates the pres-
ence of a qualitative or quantitative platelet
disorder.
THROMBOCYTOPENIA
Thrombocytopenia may be caused by in-
creased platelet destruction, decreased platelet
production or sequestration of platelets.
P
urpura results from the extrava-
sation of blood from the vascula-
ture into the skin or mucous
membranes. Therefore, purpuric
lesions do not blanch with pres-
sure. Depending on their size, purpuric
lesions are traditionally classified as petechiae
(pinpoint hemorrhages less than 2 mm in
greatest diameter), purpura (2 mm to 1 cm)
or ecchymoses (more than 1 cm).1 Although
purpura itself is not dangerous, it may be the
sign of an underlying life-threatening disor-
der. This article reviews the etiology of pur-
pura in children and suggests an approach to
evaluating the problem.
Normal He