Disorders of platelet adhesion to subendothelial collagen

            (This process requires presence of adequate VWF and GP Ib)

Bernard Soulier disease (Giant PL syndrome)

• Autosomal recessive disorder
• More than 23 mutations have been identified
• Decreased amount / abnormal function of PL membrane glycoprotein Ib /IX which leads to failure to bind to vWF
• Peripheral smear
  • Large platelets - 2.5 to 8 µ
  • Mild to moderate thrombocytopenia
  • Platelets have increased number of dense granules.
• Bone marrow- Megakaryocytes are normal

Platelet type Von Willebrand disease

• Mutation of GP1AB gene because of which there is increased binding of vWF to GPIb alpha which leads to clearance of large vWFmultimers and platelets from the circulation
• Discussed in coagulation disorders section.

Disorders of Platelet Aggregation

(Aggregation requires binding of fibrinogen and glycoprotein IIb / IIIa receptor on platelet membrane)

Glanzman’sthrombasthenia

• Autosomal recessive disorder – Gene on Chromosome  17q
• Deficiency of GP IIb / IIIa complex 
• 2 types
  • Type I – Complete absence – severe symptoms
  • Type II – Markedly reduced GP IIb / IIIa complex  and associated with less severe symptoms
  • Variant - > 50% GP IIb / IIIa complex. Symptoms are variable
• Congenital afibrinogenemia
• Defect in platelet ADP receptor
• Selective impairment of adrenaline receptors
• Thromboxane A2 receptor defect
• PAF receptor defect
• G alpha Q deficiency
• G alpha S hyperfunction
• Deficiency of G alpha I1, PLC beta2, PKC delta

Disorders of Platelet secretion

• Deficiency of Dense Granules (Storage Pool Disease)
  • Autosomal recessive 
    • Chediak Higashi syndrome
    • Hermansky – Pudlak syndrome 
      • Autosomal recessive disorder
      • 11 subtypes based on 11 different mutations
      • All these mutations result in defective lysosome biogenesis.
      • Defects are noted in lysosome related organelles which include: melanosomes, platelet dense bodies, Weibel-Palade bodies of endothelium, lamellar bodies in alveolar type II pneumatocytes, and granules proteins of certain lymphocytes.
      • Associated with  oculo cutaneous albinism, rotary nystagmus, pulmonary fibrosis and granulomatous colitis
      • Morphology: Infiltration with ceroid (lipofuscin) pigmented reticuloendothelial cells in lungs, lymph node, liver and colonesting.
      • D/D: Chediak Higashi syndrome, Griscelli syndrome
      • Diagnosis is done by platelet function study, followed by genetic 
      • Treatment
        • Lifelong sun protection
        • Treatment of visual impairment with galsses
        • For severe bleeding complaints- Platelet transfusion (Use judiously to avoid alloimmunization)
        • Granulomatous colitis- Systemic steroids/ Anti TNF agents
        • Pulmonary fibrosis: Lung transplantation
    • Wiscott – Aldrich syndrome
  • Autosomal Dominant
• Defects in pathway of thromboxane A2 synthesis
  • Deficiency of cyclooxygenase (Platelet aggregation tests similar to above)
• Gray platelet syndrome (α-storage pool disease)
  • Mutation of NBEAL2 gene
  • Deficiency of α-granules and lysosomal granules
  • Platelet aggregation tests are normal
  • Peripheral smear: Platelets appear larger than normal, pale, ghost like oval forms. Moderate to severe thrombocytopenia.
• Disorders of platelet factor 3 release
• Quebec platelet disorder
  • Autosomal dominant
  • Abnormal proteolysis of α-granule proteins
  • Severe deficiency of platelet multimerin - a factor V binding protein
  • Abnormal epinephrine induced platelet aggregation
• Selective impairment of TX-A2 receptor
  • Defective PL aggregation in response to several agents but not thrombin
• Scott's syndrome:
  • Abnormality of platelet coagulant activity
  • Autosomal dominant, with mutation in Anoctamin-ANO-6 gene
  • Defect in microvesciculation in response to several different stimuli, hence platelets fail to facilitate thrombin generation.
  • Normally, upon activation of platelets, because of "floppase", phosphotidyl serine moves from inner portion of plasma membrane to outer portion, which accelerates coagulation. This process is defective in Scott's syndrome.
  • Presentation is like coagulation disorder with prolonged bleeding after tooth extraction or post-partum hemorrhage
  • Bleeding time is normal
  • PT is prolonged.
  • Platelet function studies- Normal
  • Treatment:
    • Platelet transfusions during the event of bleeding
    • Prothrombin complex concentrates- To bypass some of coagulation steps. 
• Abnormalities of transcription factors
  • RUNX1 mutation-  High risk of MDS/AML
  • GATA1
    • X linked syndrome
    • Associated with dyserythropoiesis, anemia, thrombocytopenia, and large platelets.
    • Platelets have reduced number of alpha granules.
  • FLI1- Paris Trousseau syndrome (Refer congenital thrombocytopenia)

Clinical Features:

• Bleeding at muco-cutaneous sites
• Ecchymosis, petechiae
• Epistaxis
• Gingival hemorrhage
• Menorrhagia

Investigations:

• BT is prolonged with normal PL count
• Mean platelet volume
• Peripheral smear
• Platelet aggregation tests
  • Glanzman's
    • No response to – ADP, epinephrine, collagen
    • Normal aggregation - Ristocetin
    • Clot retraction test is abnormal
  • Bernard Soulier Syndrome
    • Normal with ADP, collagen, epinephrine
    • Abnormal with restocetin
    • (Addition of VWF does not correct restocetin aggregation. In vWD this gets corrected)
  • Storage pool disease
    • Abnormal with ADP, epinephrine, and low concentration of collagen (Primary wave is present but no secondary aggregation)

• Aperture closure time (PFA-100)- Prolonged
• Clot retraction- Absent/ reduced
• Flow cytometry for quantitative expression of platelet receptors
• Electron microscopy
• NGS- Not always useful as many involved genes are yet to be discovered

Prognosis:

• Survival is good
• About 4% of patients die because of hemorrhage 

Differential Diagnosis:

• Von- Willebrand disease
• Afibrinogenemia
• Acquired platelet disorders 

Treatment:

• General measures
  • Avoid trauma
  • Regular dental care to avoid gingival bleeding
  • Avoid aspirin
  • OC pills to avoid menorrhagia
  • Local measures like firm pressure/ nasal pack in case of epistaxis
  • Topical tranexamic acid, thrombin (botroclot)
  • Oral/IV tranexamic acid
  • Iron and folic acid supplementation
  • Severe menorrhagia- Mirena insertion/ endometrial ablation
• Drugs
  • DDAVP – 
    • IV/ SC/- 0.3microgram/Kg
    • Intranasal- 300microgram
    • Transiently increases  factor VIII & VWF levels
    • Can cause vasomotor disturbances- headache, tachycardia and facial flushing
    • Can also lead to water retention, hyponatremia and rarely seizures. Hence fluid restriction must be adviced for 24 hours.
  • Recombinant F VIIa- Useful during severe bleeding episodes/ if platelet transfusions fail to control bleeding
• Platelet Transfusion
  • Used for controlling severe hemorrhage
  • To avoid bleeding during surgical procedures
  • HLA matched PLs should be used along with WBC filters
• BMT  – Restores normal Megakaryopoiesis
• Gene therapy- Being tried in Wiskott Aldrich Syndrome

Acquired Qualitative Platelet Disorders

• Uremia- Refer to consultative hematology section
• Hematological disorders
  • Myeloproliferative disorders- Platelet dysfunction is common especially in ET
  • Dysproteinemia, multiple myeloma, macroglobulinemia:  Paraproteins coat the platelet surface and interfere with membrane reactions of platelet stimulation
• Drugs
  • NSAIDs and Aspirin: 
    • They irreversible acetylatecyclooxygenase enzyme there by prevents formation and release of thromboxane A2 
    • Enzyme activity returns as new platelets are produced and becomes normal after 7 days. 
    • Discontinuation should be balanced against increased risk of arterial thrombosis. 
    • For minor procedures such as dental/ dermatological/ cataract surgery, do not stop aspirin. 
    • For others stop 5-7 days prior to surgery and restrat 12-24hrs after surgical bleeding has ceased. 
    • If recent bare stents, defer stopping antiplatelets for at least 6 weeks. If drug eluting stents avoid stopping aspirin for at least 6 months.
  • Thienopyridines: Ticlopidine, clopidogrel, prasugrel
  • Antibiotics- Penicillins, Cephalosporins, Nitrofurantoin
  • Fibrinolytics
  • Heparin
  • Volume expanders- Dextran, hydroxyethyl starch
  • Psychotropic agents- SSRI
  • Herbal medications
• Food additives
• Alcohol
• Cardiopulmonary bypass surgery
  • As platelets become activated temporarily by abnormal surface to which they are exposed and also due to hypothermia.
• Antiplatelet antibodies (ITP- Primary/ secondary)
  • Hence bleeding may be disproportionate to the platelet count.
  • Do not assume platelet count of >30,000/cmm, is always safe.
• Hypothermia: Core body temperature <35 degree C.