Hey guys...I was wondering what would be the buzz words in differentiating this two on a clinical scenario.
ITP: GpII/IIIb def.
TTP: ADAMTS 13 def, Schistocytes, Increases LDH.
Just trying to get an idea of how they would want us to differentiate on the test.
2. Do we need to know which disease cause Intravasc defect and extravasc defect. If so, does anyone have a easy way to remember that.
Thanks!
1. Aside from having similar lab values in regards to PC (decreased) and BT (increased), the clinical pictures of the two are pretty distinct. ITP typically results after an URI and can present with chronic, somewhat smoldering hemolytic anemia. It is typically acute and relatively violent (although self-resolving) in children. From what I've been asked in question banks, expect ITP after an upper respiratory infection. With TTP, the patients have the classic pentad: fever, CNS disturbances, acute renal failure, thrombocytopenia (hence the aforementioned low PT) and
microangiopathic hemolytic anemia. Schistocytes are present, as well as an elevated lactate dehydrogenase, and these can be used to help diagnose TTP in addition to using the classic pentad of symptoms.
2. Think about it conceptually. If RBCs are coated with IgM, since it is a pentameric molecule, it is the most potent activator of the complement system. As a result, complement is activated and the hemolysis is intravascular. This can also occur with PNH (paroxysmal nocturnal hemoglobinuria), where the RBCs lack all GPI-linked surface proteins (CD55 / CD59) with a resulting inability to inhibit complement activation. This results in intravascular hemolytic anemia. Glucose-6-phosphate dehydrogenase deficiency is also an intravascular hemolysis (the oxidant stress results in RBC lysis). When RBCs are tagged with IgG, they migrate through the bloodstream and end up in the splenic reticuloendothelial system. The resident splenic macrophages bind the Fc portion of IgG and phagocytose the RBC, resulting in an extravascular hemolysis. Hereditary spherocytosis and sickle cell anemia also result in extravascular hemolysis. The mechanism of HS is due to decreased deformability of the RBC, which gets stuck in the splenic sinusoids, and ruptures or is phagocytosed. Sickle cell anemia has a similar mechanism. Bottom line, if you think about the mechanism of the respective disease, it makes it much easier. If RBCs are being chewed up while passing through a mechanical valve, naturally that's an intravascular hemolysis. That's the way I typically try and go about it.
I'm sure you probably already knew all of this, but hope this helps.
