Patho Flashcards
Excessive bleeding can result from:
- Vessel abnormalities
- Platelet abnormalities (deficiency or dysfunction)
- Coagulation derangements
Primary Hemostasis
- Platelet/ vascular problem
- Onset: spontaneous, immediate after trauma
- Sites: skin, mucous membranes
- Form: petechiae, ecchymosis
- Mucous membrane: common (nasal, oral, GI, GU)
- Other sites: rare
- Clinical examples: Thrombocytopenia, platelet defects, vWD, scurvy
Secondary Hemostasis
- Coagulation factor problem
- Onset: delayed after trauma
- Sites: Deep tissues
- Form: hematomas
- Mucous membrane: less common
- Other sites: joint, muscle, CNS, retroperitoneum
- Clinical examples: Factor deficiency, liver disease, acquired inhibitors
Vascular abnormalities
- Infections
- Drug reactions (often related to hypersensitivity vasculitis due to immune complex deposition)
- Scurvy, Ehler-Danlos (collagen defects in vessel walls)
- Henoch-Schonlein purpura (immune complex deposition)
- Hereditary hemorrhagic telangiectasia (Weber-Osler-Rendu Syndrome - dilated tortuous vessels that bleed easily
- Amyloidosis (weakens vessel walls)
Causes of thrombocytopenia
Decreased production
Decreased survival
Sequestration
Dilution
Immune thrombocytopenia
> Destruction caused by deposition of antibodies or immune complexes on platelets
>Can be autoantibodies (recognize self antigens)
>Can be alloantibodies
Where do alloantibodies for thrombocytopenia come from?
> Can arise when platelets are transfused
Can arise when platelets cross placenta
>IgG from mother can cause fetal thrombocytopenia
Non-immune causes of decreased platelet survival in thrombocytopenia
> Mechanical injury- heart valves
Disseminated intravascular coagulation (DIC)
Thrombotic microangiopathies
Chronic Immune Thrombocytopenic Purpura (ITP)
> Caused by autoantibody mediated platelet destruction
|»_space;Primary or idiopathic (diagnosis of exclusion)
Secondaries for Chronic ITP
> Systemic lupus erythematosis
HIV
B-cell neoplasms such as chronic lymphocytic leukemia
Many others
Pathogenesis of chronic ITP
> Autoantibodies most often directed against platelet surface glycoproteins IIb/IIIa or Ib-IX (typically IgG)
Anti-platelet Ab act as opsonins
>IgG Fc receptor recognition by macrophages in the reticuloendothelial system (spleen)
>Megakaryocytes may also be affected → further thrombocytopenia
>Splenectomy seems to help many patients (no more phagocytosis or autoantibody)
Clinical aspect of chronic ITP
- Females <40
- Insidious onset
- Cutaneous bleeding (petechiae, ecchymoses, melena, hematuria, menorrhagia)
- History of…easy bruising, nosebleeds, gum bleeding, soft tissue hemorrhages (with minor trauma)
- Complications: subarachnoid or intracerebral hemorrhage
- Uncommon: splenomegaly, lymphadenopathy
Labs of chronic ITP (diagnosis of exclusion)
- low platelet count
- large platelets on peripheral blood smear
- normal or increased megakaryocytes in bone marrow
- normal PT and PTT
- platelet autoantibody tests
Treatment/prognosis of chronic ITP
> glucocorticoids (inhibit phagocyte function) (may respond, many relapse)
spontaneous remission within one or more years possible
splenectomy for severe thrombocytopenia (increased risk of infections)
immunomodulation (if splenectomy fails or is contraindicated)
>IVIG
>rituximab (anti-CD20 antibody)
peptides mimicking thrombopoietin (TPO-mimetics)
Acute ITP
- mainly in children
- likely triggered by viral illness (1-2 weeks post-illness)
- self-limited mostly
Mechanisms of drug-induced thrombocytopenia
Direct destruction
Immune-mediated destruction
Drug instigates autoantibody (rarer)
Most common drugs causing drug-induced thrombocytopenia
> Bind platelet glycoproteins (IIb/IIIa)→ antibody recognition of antigenic determinants
>Quinine
>Quinidine
>Vancomycin
Heparin-induced thrombocytopenia (HIT)
Potentially deadly, arterial and venous thrombosis, limb loss or threatened loss, and/or pulmonary thromboembolism
Two types of HIT
> Type I: not usually clinically significant
>Rapid onset after therapy, likely secondary to platelet aggregating effect
Type II: (clinically significant - less common)
>Occurs 5-14 days after therapy initiation, sooner if pre-sensitized
Type II HIT
> Causes (paradoxical) thrombosis, not bleeding
(unfractionated heparin, but may still occur with LMWH -
almost never occurs with fondaparinux)
Mechanism
>Antibodies to heparin-platelet factor 4 (PF4) complex
»>PF4 is produced by activated platelets
>Antibody binding causes further platelet activation, even if thrombocytopenia
>Get aggregation and consumption, leads to prothrombotic state
HIV-Associated thrombocytopenia pathophysiology
> CD4 and CXCR4 on megakaryocytes
(can become HIV-infected >
leads to apoptosis and impaired platelet production)
B-cell hyperplasia/dysregulation leading to autoantibody formation against platelet GPIIb-IIIa (destruction in spleen)
Thrombotic Microangiopathies
> Caused by insults that lead to excessive platelet activation
>Deposit as thrombi in small blood vessels
>Cause microangiopathic hemolytic anemia
>Leads to widespread organ dysfunction
>Results in thrombocytopenia secondary to consumption
PT, PTT usually normal
Thrombotic Thrombocytopenic purpura (TTP) pentad
Fever microangiopathic hemolytic Anemia Thrombocytopenia Renal insufficiency Neurologic symptoms (FATRN)
Hemolytic-uremic syndrome (HUS)
- Children
- Lacks fever and neurologic symptoms
TTP pathophysiology
> ADAMTS13 (vWF metalloprotease) deficiency
>ADAMTS13 is normally responsible for degrading very high-molecular-weight multimers of von Willebrand factor (vWF)
>Without degradation, persistent multimers promote platelet activation and aggregation
Acquired form of TTP
- More frequent
- Typically due to autoantibody that inhibits ADAMTS13
Hereditary form of TTP
- Onset typically in adolescence, episodic symptoms
- Endothelial cell injury caused by other conditions may instigate or aggravate TTP
HUS pathophysiology
-Normal levels of ADAMTS13
-Typical: gastroenteritis with E. Coli
»produces Shiga-like toxin>
absorbed into circulation from damaged/inflamed GI mucosa >alters endothelial cell function >leads to platelet activation and aggregation
-Atypical: associated with defects, inherited or acquired, in:
»complement factor H (CFH)
»membrane cofactor protein (MCP or CD46)
»complement factor I (CFI)
»basis of platelet activation is unclear
HUS clinical/symptoms/treatment/pronosis
-Typical
»Mostly children and older adults
»Present with bloody diarrhea, followed by HUS a few days later
»Complete recovery with supportive care, but some may have irreversible renal damage or death
-Atypical
»Often remitting, relapsing course
»Treatment:
-Antibodies that inhibit activation of complement factor 5 for some inherited forms
-Immunosuppression for those with inhibitory autoantibodies
Bernard-Soulier Syndrome
- Inherited adhesion defect
- Autosomal recessive
- deficiency in GPIb
- clinically significant bleeding
- Labs: markedly increased platelet size, moderate decrease in numbers
Glanzmann thromboasthenia
- Inherited aggregation defect
- Autosomal recessive
- Deficiency or dysfunction in GPIIb/IIIa
- bleeding tendency can be severe
- Labs: platelets normal in number and size, solo w/o clumping
Secretion defects of storage pool disorders
Hermanski-Pudlak syndrome
Chediak-Higashi syndrome
Acquired platelet function disorders
Aspirin or nonsteroidal anti-inflammatory drugs
-Inhibits COX»_space; required for TXA2
-Aspirin = irreversible inhibitor
Uremia
-impairs adhesion, aggregation, and granule secretion
Thrombin activates factors…
XI, V, and VIII
Factor VIII made in….
Liver sinusoidal and Kupffer cells and other areas
vWF made by…and is circulated and secreted into…
endothelial cells and megakaryocytes; subendothelial matrix
vWF plays a role in primary and secondary hemostasis, which involve ________ and ___________, respectively
platelet adhesion; stablizing fVIII
Von Willebrand Disease (VWD)
- Most common inherited bleeding disorder
- Generally associated with mild bleeding tendency
- Clinically and molecularly heterogeneous
- Mostly autosomal dominant, but rare autosomal recessive forms
- VWF gene on chromosome 12p
Type 1 VWD
- quantitative defects
- Most common
- Autosomal dominant (spectrum of mutations, including point substitutions that interfere with maturation or result in rapid clearance)
- Mild to moderate vWF deficiency, generally mild disease
Type 3 VWD
- quantitative defects
- Autosomal recessive (usually deletions or frameshift mutations involving both alleles)
- Very low levels of vWF, correspondingly severe clinical disease (some bleeding characteristics of hemophilia due to decreased stability of factor VIII)
Type 2 VWD
- Qualitative defects
- 2A (most common, autosomal dominant, normal quantities of vWF > missense mutations lead to defective multimers)