Idiopathic Thombocytopenic Purpura Flashcards
what does ITP stand for?
diopathic thrombocytopenic purpura
also called immune thrombocytopenic purpura
what is ITP?
an acquired form of thrombocytopenia in which patients produce antibodies that bind to their own platelets, marking them for destruction in the spleen
the platelet count drops, and eventually there are not enough platelets to participate in normal clotting
what is purpura?
large areas of bleeding within the skin
looks like blood big freckles
what are the two forms of ITP?
acute and chronic ITP
what is chronic ITP?
slow onset with mild symptoms like petechiae, nosebleeds, easy bruising and excessive menstrual flow
bleeding is relatively minor
life threatening bleeding is rare, especially if you’re getting treated
what are the types of chronic ITP?
- primary = unrelated to any known risk factors
- secondary = occurring in the setting of other conditions like lupus, HIV or hematologic malignancy called chronic lymphocytic leukemia
what conditions can cause secondary chronic ITP?
- lupus
- HIV
- hematologic malignancy called chronic lymphocytic leukemia
what population is usually effected by chronic ITP?
mostly in adult women under the age of 40
what population nis usually effected by acute ITP?
children
and usually happens following a viral illness
what is acute ITP?
abrupt onset ITP
sudden appearance of a petechial rash, bruising, or bleeding, the child usually looks and feels well
the disease is self-limiting. With or without treatment, most children completely recover within a few months
what’s the pathogenesis of ITP?
patients make antibodies that bind to their own platelets
the antibodies bind to platelet glycoproteins, such as glycoprotein IIb/IIIa
anything covered in antibodies looks like food to macrophages so in ITP the macrophages in the spleen destroy the antibody-coated platelets
what is opsonization?
the process of coating cells with antibodies
why is the body generating antibodies against its own platelets in ITP?
- sometimes, the patient has had a recent viral illness, and the antibodies generated to fight the virus just happen to cross-react with the patient’s platelets
- the patient has a pre-existing autoimmune disease, like lupus, in which normal immune processes have gone awry, and antibodies are made against all sorts of “self-antigens,” including those on platelets
- idiopathic
How do the antiplatelet antibodies damage the platelets in ITP?
They coat (“opsonize”) the platelets, which makes them appear yummy to macrophages in the spleen.
what does the blood smear of ITP show?
isolated thrombocytopenia = platelets are decreased in number but everything else is fine!
occasionally, some of the platelets may be larger than normal, but otherwise, the platelets do not appear abnormal
what’s the number of platelets in thrombocytopenia?
minor: 100,000 – 149,000/mmˆ3
severe: <10,000/mmˆ3
what does the bone marrow in ITP look like?
increased number of megakaryocytes, many of which are smaller than normal, with just a single nucleus instead of the usual multinucleated huge megakaryocytes seen in normal bone marrow biopsies
what tests do you do to diagnose ITP?
there are no specific laboratory tests or diagnostic criteria that can be used to prove that ITP is present…
you can’t look for anti-platelet antibodies because the antibody tests have a very low sensitivity so the tests are useless and doctors don’t even do them
how do you diagnose ITP?
- patient must have isolated thrombocytopenia
- you also have to show that there isn’t another apparent cause for the thrombocytopenia
ITP is a diagnosis of exclusion
what are some other causes of an isolated thrombocytopenia other than ITP?
- Pseudothrombocytopenia (a falsely low platelet count due to things like an insufficiently anticoagulated specimen)
- Infection (such as HIV, hepatitis C, and EBV)
- Hypersplenism (a big spleen can “trap” platelets, making the peripheral count
appear low) - Pregnancy-related thrombocytopenia
- Medication-related thrombocytopenia
what is isolated thrombocytopenia?
low platelets BUT RBC and WBC are totally normal
how do you treat ITP?
treatment is typically given to patients with severe bleeding or with really, really low platelet counts like <10,000
- glucocorticoids (steroids)
- IV immune globulin
- platelet transfusions
- splenectomy if no other treatment works so you can remove the source of platelet destruction
what, if present in a patient, would rule out the diagnosis of ITP?
Hb = 9.2 g/dL
to diagnose ITP, the thrombocytopenia must first be isolated meaning there are not any other abnormalities in blood counts, such as a low hemoglobin, which should lead you in a different diagnostic direction
