Autoimmune Idiopathic Thrombocytopenic Purpura (ITP) Nicola Davis
ITP w Clinical syndrome in which a decreased number of circulating platelets presents as a bleeding tendency, easy bruising, or extravasation of blood from capillaries into skin and mucous membranes
w The thrombocytopenia seen in ITP is due to immune destruction of platelets. w Abnormal antibody binds to circulating platelet membranes. w The immunoglobulin coated platelets induce phagocytosis primarily in the spleen. w Thrombocytopenia develops if the bone marrow is unable to increase production of platelets to compensate for the destruction.
Acute ITP w Usually seen in children w Peak incidence 3 -5 years w M = F w Usually occurs ~ 2 weeks following a viral infection w Often self limiting
Chronic ITP w Usually seen in adults w Peak incidence 30 - 40 years w Onset in patient >60 years is uncommon w F:M = 3:1 w US incidence = 1/10,000 annually w Usually idiopathic but may occur in association with other autoimmune disorders, in patients with CLL and after viral infections
Clinical Features w Easy bruising w Purpura w Epistaxis w Menorrhagia w Major haemorrhage is rare w Splenomegaly is rare
Investigations w Diagnosis of exclusion w FBC isolated thrombocytopenia anaemia or neutropenia may indicate other diseases - though may be iron deficiency anaemia from chronic blood loss in chronic ITP w Blood Smear morphology of platelets is typically normal with varying numbers of large platelets morphology of RBCs and leukocytes should be normal
w Bone Marrow normal or increased numbers of megakaryocytes otherwise normal w Antiplatelet Antibodies if -ve does not rule out ITP not essential for the diagnosis of ITP
Treatment w In children: Treatment depends on bleeding risk Platelets > 30 can be managed without specific treatment Platelets < 20 are given oral prednisone 1mg/kg/day. May also be given high dose IV Ig causing a transient rise in platelet levels.
Treatment w In Adults: Platelets > 50 have a low risk of haemorrhage and no specific treatment is needed Platelets < 30 are treated with oral prednisone 1mg/kg/day. (Improvement seen in a few days) Platelets < 5 are high risk and should be treated with methylprednisolone and Ig Platelet transfusions may be used to control bleeding acutely
Surgical Options w Splenectomy usually results in rapid, complete, lifelong remission in acute ITP 90% of chronic ITP respond following splenectomy, although ~ 30% of these eventually relapse There is a lifelong risk of sepsis from encapsulated bacteria following splenectomy so will need immunisation against H. influenzae type B and S. Pneumoniae - boost every 5 years.
Treatment-Resistant ITP w In those patients who do not respond to corticosteriods or splenectomy immunosuppresive drugs may help: azathioprine cyclophosphamide vincristine danazol a non-virilising androgen may also help anti-CD20 (rituximab)
Prognosis w Children: >80% with untreated ITP have spontaneous recovery in 2-8 weeks Treatment with prednisone and Ig accelerates the increase in platelet count decreasing the chance of serious haemorrhage
Prognosis w Adults: 60 - 90% of adults have an increased platelet count after treatment with prednisone and Ig Of those who have a splenectomy ~65% have a sustained response and 10 - 15% have a partial response