Thrombocytopenia, Immune-Mediated
Basic Information 
Clinical Presentation
History, Chief Complaint
• Multiple sites of small vessel bleeding
• Bleeding possibly confined to a single system such as the respiratory system with epistaxis or hematomas in the nasal sinus
• May be generalized with widespread petechial hemorrhages on the mucous membranes, epistaxis, and melena
• Obvious bruising or hematoma formation
Etiology and Pathophysiology
• Antibodies coat the platelet surface and cause their premature removal.
• In primary immune-mediated thrombocytopenia (IMTP), immunoglobulin (Ig) G antibodies produced in the spleen bind to platelet membranes. These antibodies may also bind to megakaryocyte membranes.
• In secondary IMTP, platelets may bind immune complexes formed by antibodies binding to a drug, virus, or neoplastic antigen.
• Removal of the offending antigen may cause rapid remission of secondary IMTP.
• Secondary to equine infectious anemia (see “Anemia, Equine Infectious” in this section), lymphosarcoma, or autoimmune hemolytic anemia
Diagnosis 
• Clinical diagnosis usually apparent
• Small-vessel hemorrhagic diathesis
• Severe thrombocytopenia with no evidence of disseminated intravascular coagulation (DIC)
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