Immune thrombocytopenic purpura

Background
  • Abbreviation: ITP
  • Known as both "idiopathic" or "immune" thrombocytopenic purpura
  • Acquired autoimmune disease resulting in destruction of platelets
  • Because circulating platelets are functional, life-threatening bleeding only once platelet count <10K
  • Chronically, the disease follows a course that is usually stable with intermittent and episodic flares, leading to clinically relevant thrombocytopenia[1]

Types
Charateristic Acute ITP Chronic ITP
Common age groupYounger childrenAdults
SexAffects men/women equallyUsually women
DurationResolves in 1-2 monthsLasts > 3 months
CauseTypically follows viral illnessMore likely to have an underlying disease or autoimmune disorder (e.g. SLE)
PrognosisRarely remits spontaneously or with treatment

Clinical Features

Differential Diagnosis

Thrombocytopenia

Decreased production

Increased platelet destruction or use

Drug Induced

Comparison by Etiology
ITP TTP HUS HIT DIC
↓ PLT YesYesYesYesYes
↑PT/INR NoNoNo+/-Yes
MAHA NoYesYesNoYes
↓ Fibrinogen NoNoNoNoYes
Ok to give PLT YesNoNoNoYes

Petechiae/Purpura (by cause)

Evaluation
  • Diagnosis of exclusion
  • Must differentiate acute ITP from chronic ITP, which suggests an underlying disorder
  • CBC shows normal cell lines except for the platelets (may have mild anemia)

Management

Options
  • First choice in adults: Corticosteroids
    • Prednisone 60-100mg/d with taper after count reaches normal (50-75% remission rate by 3 wks)
    • Methylprednisolone 30mg/kg/d IV x 3 days (for life-threatening bleeding)
  • First choice in children: Intravenous Immunoglobulin G (IVIG) 1gm/kg/d x 2 days
  • High dose Anti-D (RhoGAM): patient must be Rh+ for it to work
    • Causes shift towards splenic destruction of antibody-coated Rh+ RBCs
    • Thereby has less functional capacity to destroy platelets
    • Dosage dependent on Hb level in mg/dL[2]
      • Hb>10, 250 IU/kg IV x1 over 5min
      • Hb<10, 125 IU/kg IV x1 over 5min
  • Platelet transfusion
    • Indicated for life-threatening bleeding
    • Will ultimately be destroyed
    • Transfuse only following first dose of methylprednisolone or IVIG
      • Holding transfusion until after first dose results in greater rise in platelet count
      • Calculate number of packs needed to increase count to over 50k (1 pack generally increases by 10k)
  • Estrogen for uterine bleeding: 25mg IV x1

Indications

Adults

Children

Other Options
  • Splenectomy if above fails (only 2/3 effective)
  • Rho(D) Immune Globulin (RhoGAM)
    • Will induce mild hemolysis in Rh+ patients that decreases macrophage activity
    • Spleen will not destroy platelets covered in antibodies
  • Rituximab
    • May help as ITP is autoimmune process

Disposition
  • Admit: platelet count <20K or significant mucous membrane bleeding
  • Discharge: platelet count >20K AND asymptomatic OR only minor petechiae

Complications

See Also

References
  1. Cines DB and Blanchette VS. Immune Thrombocytopenic Purpura. New England Journal of Medicine. Vol 346 (13); 995-1008.
  2. eMedicine. RhoGAM. http://reference.medscape.com/drug/rhogam-hyperrho-s-d-rho-d-immune-globulin-343143.
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