USMLE (Subject) / Kaplan - Pathology (Lesson)

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Kaplan

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  • Histochemical stains Prussian blue – iron Congo red – amyloid Acid fast (Ziel-Neelsen, Fite) – acid-fast bacilli Periodic acid Schiff (PAS) – high carbohydrate content molecules Trichrome – cells and connective tissues Reticulin – collagen type III molecules
  • Antibody stains Cytokeratin – epithelial cells Vimentin – cells of mesenchymal origin except the 3 muscle types; stains many sarcomas Desmin – smooth, cardiac, and skeletal myosin
  • Hematoxylin and Eosin Hematoxylin: Stains blue to purple- Nucleus and nucleolus- Calcium- Bacteria Eosin: Stains pink to red- Cytoplasm- Collagen- Fibrin- RBCs- Thyroid colloid
  • Contents of platelet granules Alpha granules:- Fibrinogen- Fibronectin- Factor V and vWF- Platelet factor 4- PDGR Dense bodies:- ADP- Ca2+- Histamine and serotonine- Epinephrin
  • Immune thrombocytopenia purpura (ITP) Immune-mediated attack (usually IgG antiplatelet antibodies) against platelets leading to decreased platelets (thrombocytopenia) which result in petechiae, purpura (bruises), and a bleeding diathesis (eg, hematomas). - Antiplatelet antibodies against platelet antigens such as GpIIb-IIIa and GpIb-X (type II hypersensitivity reaction)- Antibodies are made in the spleen and the platelets are destroyed peripherally in the spleen by macrophages, which have Fc receptors that bind IgG-coated platelets. Acute ITP: Seen in children following a viral infection and is self-limitingChronic ITP: Usually seen in women in their childbearing years and may be the first manifestation of SLE. Labs:- Decreased platelet count, prolonged bleeding time- Normal prothrombin time and partial thromboplastin time- Peripheral blood smear: thrombocytopenia with enlarged immature platelets (megathrombocytes) Treatment: Corticosteroids, splenectomy
  • Thrombotic thrombocytopenic purpura (TTP) Rare disorder of hemostasis in which there is a widespread intravascular formation of fibrin-platelet thrombi. It is sometimes associated with an acquired or inherited deficiency of the enzyme ADAMTS13, responsible for cleaving large multimers of von Willebrand factor. - Often affects adult women- Inclusion criteria: Microangiopathic hemolytic anemia and thrombocytopenia, with or without renal failure or neurological abnormalities.- Widespread formation of platelet thrombi with fibrin (hyaline thrombi) leading to intravascular hemolysis (thrombotic microangiopathy) Labs:- Decreased platelet count, prolonged bleeding time- Normal prothrombin time and partial thromboplastin time- Peripheral blood smear: thrombocytopenia, schistocytes, reticulocytosis Treatment: plasma exchange
  • Hemolytic uremic syndrome (HUS) Thrombotic microangiopathy due to endothelial cell damage. - Occurs mostly in children, typically after a gastroenteritis (typically due to Shiga toxin-producing E coli 0157:H7) - Abdominal pain, diarhhea- Microangiopathic hemolytic anemia- Thrombocytopenia- Renal failure (more commonly than in TTP) - Kidneys show fibrin thrombi in the glomeruli
  • Coagulation factors The intrinsic pathway is activated by the contact factors, which include:- Subendothelial collagen- High molecular weight kininogen (HMWK)- KallikreinXII → XIIa The extrinsic pathway is activated by the release of tissue factor (thromboplastin)VII → VIIa
  • Coagulation lab tests Prothrombin time (PT): Tests extrinsic and common coagulation pathways- VII, X, V, prothrombin, fibrinogen- INR standardizes the PT Partial thromboplastin time (PTT): Tests instrinsic and common coagulation pathways- XII, XI, IV, VIII, X, V, prothrombin, fibrinogen Thrombin time (TT): Tests for adequate fibrinogen levels Fibrin degradation products (PDP): Tests fibrinolytic system (increased with DIC)
  • Thrombus vs blood clot Thrombus- Location: Intravascular- Composition: Platelets, fibrin, RBCs and WBCs- Lines of Zahn: Present- Shape: Has shape Blood clot- Location: Extravascular or intravascular (postmortem)- Composition: Lacks platelets, fibrin, RBCs and WBCs- Lines of Zahn: Absent- Shape: Lacks shape
  • Major causes of shock Cardiogenic shock (pump failure): myocardial infarction, cardiac arrhythmias, pulmonary embolism, cardiac tamponade Hypovolemic shock (reduced blood volume): hemorrhage, fluid loss secondary to severe burns, severe dehydration Septic shock (viral of bacterial infection): causes cytokines to trigger vasodilation and hypotension, ARDS, DIC, multiple organ dysfunction syndrome Neurogenic shock (generalized vasodilation): anesthesia, brain or spinal cord injury Anaphylactic shock (generalized vasodilation): type I hypersensitivity reaction
  • Atherosclerosis Earliest (clinically reversible stage): Fatty streak - Grossly: yellow intimal streak and characterized - Microscopically: lipid-laden macrophages (foam cells) - Stable atheromatous plaques: Dense fibrus cap, small lipid core, less inflammation. Cause chronic ischemia. - Vulnerable atheromatous plaques: At risk for rupture, thrombosis or embolization due to composition (thin fibrous cap, large lipid core, dense inflammation).
  • Mönkeberg medial calcific sclerosis Medial calcification of medium-sized (muscular) arteries, such as femoral, tibial, radial, and ulnar arteries. - Asymptomatic, but may be detected by x-ray.
  • Arteriolosclerosis - Affects small arteries and arterioles. - Hyaline arteriolosclerosis: pink, glassy arterial wall thickening with luminal narrowing seen in benign hypertension, diabetes, and aging- Hyperplastic arteriolosclerosis: smooth-muscle proliferation resulting in concentric ("onion skin") wall thickening and luminal narrowing seen in malignant hypertension
  • Syphilitic aneurysms Involve the ascending aorta in tertiary syphilis.  Syphilitic aortitis causes an obliterative endarteritis of the vasa vasorum, leading to ischemia and smooth-muscle atrophy of the aortic media. Syphilitic aneurysms may dilate the aortic valve ring, causing aortic insufficiency.
  • Vascular ectasias Nevus flammeus nuchae: Neck "birthmark" or "stork bite" that regresses. Port wine stain: Vascular birthmark that does not regress. Spider telangiectasias: Occur on the face, blanch with pressure, and are associated with pregnancy.
  • Glomus tumor Benign, small, painful tumor of the glomus body that usually occurs under fingernails.