Page 528 - Clinical Hematology_ Theory _ Procedures ( PDFDrive )

512 PART 7 ■ Principles and Disorders of Hemostasis and Thrombosis

Pathophysiology Characteristics of Immune

I une HI is cause by an antibo y that recognizes he - TABLE 26.2 Thrombocytopenia

arin boun to PF4 on the ate et sur ace (Fig. 26.7). T e

antibo y bin s to the he arin-PF4 co ex, which then New ly

a ows the antibo y to bin the Fc rece tor on the ate et. Characteristic Diagnosed Chronic

Interaction with the Fc rece tor activates the ate et that

resu ts in the oss o ate ets, thro bocyto enia, an ate et Peak age 2–5 years Adulthood

aggregation (thro bosis). A s a nu ber o cases o HI (30–60 years)

ay invo ve an antigen other than the PF4 co ex. History of infection Common Uncommon

Spontaneous remission Common Rare

Laboratory Data

In a ition to the ate et count, three s eci c aboratory y ica y, a u t I P is a chronic isease. I P in chi ren
assays can be use in atients with sus ecte HI : is a c inica y istinct isor er an is usua y acute. A ong

1. Enzy e- inke i unosorbent assay (ELISA) a u ts, I P is ost co on in young wo en (a roxi-

2. P ate et aggregation ate y 70% o atients are 10 to 40 years o ). Chronic I P is

3. Serotonin re ease a estructive thro bocyto enia cause by an autoantibo y.
A roxi ate y 80% o atients ex erience re issions a er

T e ELISA assay an serotonin re ease assay have sensi- either corticosteroi thera y or s enecto y. So e atients
tivities o ore than 90%, with very high s eci city or HI res on to other thera y; in a substantia grou o atients,

antibo y. P ate et aggregation is between 50% an 80% an the isease is re ractory to thera y.
is very s eci c.

Clinical Signs and Symptoms
Increased Utilization of Platelets
Onset is o en insi ious. Pur ura, e istaxis, an gingiva
Acce erate consu tion o ate ets is another cause o b ee ing are co on. He aturia an GI b ee ing are ess
thro bocyto enia. co on, an intracerebra he orrhage is rare. Serious

One o the ost i ortant an requent y encountere b ee ing oes not occur in ost atients.

or s o increase consu tion o ate ets is immune throm-

bocytopenia (ITP), revious y known as immune thrombocyto- Pathophysiology
penic purpura. T is antibo y-re ate res onse, which ay

be rece e by in ection, is be ieve to have a evastating T e o conce t was that thro bocyto enia resu te ro
e ect on ate et surviva . Patients su ering ro acute i io- antibo y- e iate ate et estruction. T ere are two new

athic I P usua y have a s ontaneous re ission within sev- conce ts:
era weeks o the onset o I P. However, I P ay co icate 1. T e sa e antibo ies that e iate ate et estruction a so

other antibo y-associate isor ers such as syste ic u us e iate i aire ate et ro uction by a aging ega-
erythe atosus (SLE). Patients with i uno ogica thro - karyocytes an /or b ocking their abi ity to re ease ro-

bocyto enic ur ura usua y e onstrate etechiae, bruis- ate ets. -ce – e iate e ects are be ieve to ay a ro e.
ing, enorrhagia, an b ee ing a er inor trau a. 2. en to twenty ercent o cases are not antibo y e iate .

Im m une Throm bocytopenia In acute I P, the echanis o ate et estruction is sug-

T e new stan ar no enc ature, I P, re aces the ter geste to be either by absor tion o vira antigen onto the
i io athic thro bocyto enic ur ura. I P is an acquire ate et sur ace o owe by antibo y bin ing or by or a-

i une- e iate isor er characterize by iso ate thro - tion o an i une co ex on the sur ace o ate ets via
bocyto enia ( ate et count ess than 100 × 10 /L) an the the ate et Fc (i unog obu in) rece tors. In chronic I P,
9

absence o any obvious initiating an /or un er ying cause the target or the autoanti ate et antibo ies is ate et e -
o the thro bocyto enia. I P occurs in chi ren an a u ts brane GPs (e.g., GPIIb/IIIa, GPIb/IX, GPIa/IIa, an GPIV).

an is characterize by a ow ate et count, nor a bone T e ajority o ate et autoantigens are resent on either
arrow, an the absence o other causes o thro bocyto e- GPIIb/IIIa or GPIb/IX co ex. T e echanis o autoan-

nia. Various characteristics exist in I P ( ab e 26.2). tibo y or ation is unknown.

Epidemiology Laboratory Data

I P is a air y rare, genera y benign i ness in the e iatric Iso ate thro bocyto enia is the essentia abnor a ity.

o u ation. About two-thir s o chi ren recover s onta- Diagnosis requires exc usion o other causes o thro bocy-

neous y. In a u ts, the inci ence is a roxi ate y equa or to enia. Antibo ies to s eci c ate et e brane GPs can

both gen ers exce t in the i -a u t years (30 to 60 years), be etecte in ost atients, but neither these assays nor

when the isor er is ore reva ent in wo en. I P is c as- easure ents o ate et IgG, which are o en erroneous y

si e by uration into new y iagnose , ersistent (3 to 12 re erre to as anti ate et antibo y tests, are i ortant or

onths uration), an chronic (≥12 onths). the iagnosis or anage ent.