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🌱 來自: Huppert’s Notes
Additional Details about the Platelet Destructive Processes🚧 施工中
Additional Details about the Platelet Destructive Processes
Immune Thrombocytopenic Purpura (ITP)
• Pathophysiology: Anti-platelet antibodies → Splenic macrophages consume platelet/Ab complex
• Clinical features*:* Petechiae, purpura, bleeding; NO splenomegaly
• Diagnosis:
- Isolated thrombocytopenia (platelets <20K/μl but rest of counts normal)
- Smear typically has large platelets and NO schistocytes! Megakaryocytes are present in the bone marrow.
- Diagnosis of exclusion: No antibody test. Must rule out other causes first (medication-induced, HIV, HCV, H. pylori, etc.). Do not usually have to do a bone marrow biopsy in younger patients, but must consider in older patients.
• Treatment*:*
- 1st line: Dexamethasone (40 mg x 4 days) vs. prednisone 1mg/kg/day with slow taper. IVIG 1g/kg ×2 doses may be used with steroids if a rapid platelet count rise is needed.
- 2nd line: Rituximab, TPO agonists (romiplostim); consider splenectomy if refractory
Hemolytic Uremic Syndrome (HUS)
• Pathophysiology*:* Endothelial damage caused by medications or Shiga toxin–mediated bloody diarrhea (Ecoli O157:H7, Shigella)
• Clinical features*:*
- Three classic features: 1) Microangiopathic hemolytic anemia (MAHA); 2) Thrombocytopenia; 3) Renal failure
- HUS is clinically similar to TTP, but more likely to have renal failure and less likely to have neurologic symptoms
• Diagnosis*:* Smear with schistocytes. Positive Shiga-toxin/EHEC test confirms STEC-HUS. Complement gene mutation panel evaluates for atypical (complement-mediated) HUS.
• Treatment*:* Supportive care; consider plasma exchange (“plex”) and eculizumab for atypical HUS
Thrombotic Thrombocytopenic Purpura (TTP)
• Pathophysiology*:* Deficiency in the protease ADAMTS-13 (congenital defect or acquired autoantibody), which usually cleaves vWF. The uncleaved vWF clump and bind to platelets, leading to microvascular occlusion and thrombocytopenia.
• Clinical features*:* Same as HUS + fever + neurologic symptoms (seizures, altered mental status). Patients with TTP are less likely to have renal dysfunction than those with HUS.
• Diagnosis*:* Blood smear with schistocytes. Then this is a clinical diagnosis – start treatment right away! PLASMIC score can be helpful, but neither sensitive nor specific. Order ADAMTS-13 but don’t wait for the result to initiate treatment.
• Treatment*:* Immediate plasmapheresis (“plex”)! TTP is 90% fatal without therapy. Do NOT give platelets – can precipitate further hemolysis!
Heparin-Induced Thrombocytopenia (HIT)
Type 1 (non-immune mediated)
• Clinical features**:** Drop in platelets that occurs 1–4 days post-heparin, platelets decreased but still >100K/μl
• Treatment**:** Can continue heparin; does not change clinical management
Type 2 (immune mediated)
• Clinical features**:** 5–10 days post-heparin (higher risk with unfractionated heparin than LMWH). Caused by an antibody to platelet factor 4-heparin complex, which causes the platelets to clump/clot. Platelet count falls by >50%. Can cause DVT, PE, stroke, and necrotic skin lesions at the heparin injection site.
• Diagnosis**:** Calculate “4T score” to help predict risk (see online calculators). If 4T score is ≥4, send HIT assay.
• Treatment**:** Moderate/high risk: Hold heparin products and start alternative anticoagulation (e.g., argatroban, bivalirudin, fondaparinux) right away – do not wait for HIT assay to return to switch anticoagulants! Do NOT give platelets.
Disseminated Intravascular Coagulation (DIC)
• Definition: Mixed platelet/coagulation disorder. See section below.