A nurse is caring for a patient with thrombocytopenia.
Which statement accurately describes the pathophysiology of immune thrombocytopenic purpura (ITP)?
A.
“ITP results from decreased platelet production in the bone marrow.”
B.
“In ITP, autoantibodies mark platelets for destruction by macrophages.”
C.
“ITP is characterized by impaired cleavage of von Willebrand factor.”
D.
“Thrombocytopenia in ITP is triggered by heparin-platelet factor 4 complexes.”
The Correct answer and Explanation is:
The correct answer is:
B. “In ITP, autoantibodies mark platelets for destruction by macrophages.”
Explanation:
Immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by low platelet counts (thrombocytopenia), which increases the risk of bleeding. The condition involves the immune system mistakenly attacking and destroying platelets, the blood components responsible for clotting.
The pathophysiology of ITP centers on the production of autoantibodies—typically IgG antibodies—that target platelets. These autoantibodies bind to glycoproteins on the surface of platelets, such as GPIIb/IIIa or GPIb-IX-V. Once bound, these autoantibody-coated platelets are marked for destruction. Macrophages, primarily in the spleen, recognize these tagged platelets as foreign and phagocytose (engulf and digest) them. This immune-mediated destruction leads to a significant reduction in the number of circulating platelets, causing thrombocytopenia.
The spleen also plays a key role in ITP beyond platelet destruction. It is a site where immune complexes form, and autoantibodies are produced, perpetuating the autoimmune cycle. Some patients with ITP may have an enlarged spleen due to increased activity.
This autoimmune attack on platelets is independent of platelet production in the bone marrow, which typically remains normal or increased as the body attempts to compensate for the rapid loss of platelets. However, the overproduction cannot counteract the rate of destruction.
Other choices in the question refer to different types of thrombocytopenia or clotting disorders:
- A refers to reduced platelet production, which is not the primary mechanism in ITP.
- C describes the pathophysiology of thrombotic thrombocytopenic purpura (TTP), where there’s impaired cleavage of von Willebrand factor.
- D describes heparin-induced thrombocytopenia (HIT), where antibodies form against complexes of heparin and platelet factor 4.