Today’s ambulatory report is brought to us by one of our fantastic R3’s, Dr. Ijeoma Oguike, with expert discussant, Dr. Srikanth Nagalla.
A young man with a history of hypothyroidism presented to clinic with bilateral lower extremity non-blanching petechiae. He otherwise was without any complaints. On exam, he was well appearing and without evidence of hemarthroses or hematomas. He was found to have a platelet count of less than 5,000 thousand per microliter of blood with an otherwise normal CBC. He was negative for HIV and HCV. He was diagnosed with primary immune thrombocytopenia.
Immune thrombocytopenia is an acquired autoimmune condition caused by auto-antibodies (IgG) to one of several possible surface receptors (commonly, the GIIb/IIIa receptor) on platelets. It is a diagnosis of exclusion characterized by isolated thrombocytopenia without another obvious cause. Patients often present without any symptoms but may have signs of primary hemostatic disorders (mucocutaneous bleeding).
-The differential diagnosis for an isolated platelet count in the single digits include: immune thrombocytopenia, drug-induced thrombocytopenia and post-transfusion purpura
-When immune thrombocytopenia is suspected, be sure to test for HIV and hepatitis C as several cases are linked with infection with these agents. Additional testing for other disease states can be considered in select patients with signs and symptoms of disease (e.g. ANA for connective tissue disease).
-Approximately 20% of patients with an initial diagnosis of primary immune thrombocytopenia eventually are diagnosed with secondary immune thrombocytopenia due to other underlying conditions such as autoimmune disease, CVID, lymphoma, HIV, HCV, autoimmune lymphoproliferative syndrome
–Steroids: prednisone 1 mg/kg with a prolonged taper or dexamethasone 40 mg PO daily for 4 days (mean onset of response is 2-5 days with peak effect 10-14 days)
–IVIG: mean onset of response is 1 day with peak effect in approximately 5-7 days
–Rituximab: mean onset of response 8 weeks
–Splenectomy: mean onset of response varies from immediate to weeks
–Thrombopoetin mimetics: If above steps fail, eltrombopag or romiplostim can be used with the goal of stimulation of the bone marrow to generate platelets faster than they can be destroyed. mean onset of response is 2 weeks
Note that treatment is not aimed at normalizing platelet counts. Rather, treatment attempts to achieve a goal platelet count of >50000 per microliter of blood to avoid serious bleeding
Q and A:
Q: Why do patients with immune thrombocytopenia have less bleeding relative to their platelet counts?
A: Hemostatic presentations can vary in immune thrombocytopenia. This variability is likely due to the functional effect of the autoantibody on the platelets. Some antibodies are activate platelet aggregation whereas others neutralize. Thus, some patients may tend to bleed while others will have relatively low rates of bleeding relative to their platelet count.
Q: Can plasmapheresis be used for immune thrombocytopenia?
A: Plasmapheresis is most effective for IgM mediated processes. Due to its large size, most IgM molecules are intravascular and can be removed by plasmapheresis. IgG, however, has a large volume of distribution. As such, plasmapheresis is not as effective in immune thrombocytopenia.