Immune thrombocytopenia

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Immune thrombocytopenia

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Questions

USMLE® Step 1 style questions USMLE

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A 9-year-old boy is brought to the emergency department by his parents due to prolonged bleeding following a tooth extraction earlier in the day. Past medical history is noncontributory. Temperature is 37.5°C (99.5°F), pulse is 88/min, respirations are 14/min, and blood pressure is 112/62 mmHg. Physical exam shows gingival bleeding and petechiae. Laboratory testing is obtained, and the results are shown below.  
 
Laboratory value  Result
 Hematologic  
 Hemoglobin  12 g/dL 
 Hematocrit  40% 
 Platelet count  95,000/mm3  
 Leukocyte count  9,000/mm3  
Coagulation studies  
 Prothrombin time (PT)  12 seconds 
 Activated partial thromboplastin time (aPTT)  29 seconds 
 Bleeding time*  15 minutes 
*Reference Range: 2-7 minutes  

Which of the following conditions is the patient at greatest risk of developing?   

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Immune thrombocytopenic purpura or ITP is an autoimmune condition in which the body produces antibodies against its own thrombocytes or platelets, which are destroyed. And this result in purpura, or small bleeding spots beneath the skin.

Normally, when there’s any kind of damage to the blood vessel, hemostasis occurs, which is the process that stops the bleeding and plugs the damaged vessel to limit the blood loss.

And there are two steps: primary and secondary hemostasis. During primary hemostasis, platelets aggregate to form a plug at the site of an injured blood vessel.

Platelet aggregation is mediated by surface proteins found on platelets, called GP2B3A receptors. While these platelets are aggregating, secondary hemostasis kicks in.

Secondary hemostasis is also called coagulation, because that’s when clotting factors come into play one after another, with a view to cleaving fibrinogen into fibrin.

Then, fibrin forms a protein mesh, kinda like a giant net that covers the platelet plug and stabilizes it.

Now, in ITP, the spleen produces certain IgG autoantibodies which bind to the platelet receptor Gp2B3A, and target the platelet-antibody complexes for destruction in the spleen.

This leads to lowering of platelet counts in the blood, which makes it harder for bleeding to stop. Now, ITP can be acute or chronic.

Acute ITP usually affects children, a couple of weeks after a viral infection, and resolves spontaneously within two months.

Chronic ITP usually affect females of reproductive age, and persist more than six months. Chronic ITP can also be primary, when it occurs without an underlying trigger, or secondary, when it’s triggered by another condition like hepatitis C, HIV, or lupus.

Most of the time, ITP is asymptomatic. In some cases, it can cause purpura, which are red or purple spots on the skin, measuring 0.3 to 1 cm in diameter.

Sources

  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  3. "Harrison's Principles of Internal Medicine" McGraw-Hill (2004)
  4. "Purpura thrombopénique immunologique [Immune thrombocytopenic purpura]" Rev Prat (2019)
  5. "Immune Thrombocytopenic Purpura" New England Journal of Medicine (2002)
  6. "[TREATMENT OF IMMUNE THROMBOCYTOPENIC PURPURA IN ADULTS: UPDATE]" Harefuah (2019)
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