Immune Thrombocytopenia: A Differential Diagnosis
Strategies and types of tests used by clinicians to help exclude various conditions that may present similarly to immune thrombocytopenia during a diagnostic work-up.
Bhavesh Shah, RPh, BCOP: I want to go back to the referrals and diagnosing. Now, I’m sure there’s not an actual gold standard of: This is how you diagnose ITP [immune thrombocytopenia]; here are the labs that you use. I’m curious, from both of your perspectives, how do providers diagnose ITP in your clinic?
David Hughes, PharmD, BCOP: Ultimately, ITP ends up being a diagnosis of exclusion, which is every hematologist’s or oncologist’s favorite thing to hear. A lot of physicians end up—or in clinic they end up—ordering a whole panel to rule out every other cause of that thrombocytopenia. A history and physical are important. The physical examination is probably 1 of the most critical things in working up an ITP patient. One of the first things to rule out are drugs that may cause thrombocytopenia, such as chronic exposure to certain penicillin, vancomycin, and antibiotics like those.
A peripheral blood smear can be helpful to see that. There has been talk about whether a bone marrow biopsy is always warranted. Older guidelines would say that anyone over age 60 would need a bone marrow biopsy. But typically, a bone marrow biopsy would be used to rule out myelodysplasia syndrome or its symptoms in our older population. Some patients with GI [gastrointestinal] symptoms such as H pylori [Helicobacter pylori] can have some overlap with ITP. Therefore, they’ll rule out H pylori. They also use coagulation studies, aPTT [activated partial thromboplastin time] or PT [partial thromboplastin time] levels to rule out coagulation disorders like DIC [disseminated intravascular coagulation]. A lot of these things end up being worked up as a means to rule everything else out in order to get that diagnosis of an idiopathic disease.
Ali McBride, PharmD, MS, BCOP, FASHP, FAzPA: To add to that discussion, it’s a team-based approach. The diagnosis usually comes from a benign hematologist. Sometimes it’s more the acute leukemia. In some cases, based on community-based practice, some of those general oncologists, they cover hematology and oncology. They cover everything. That’s your community-based oncology team. When you’re looking at these cases in which you have a T-cell attack on these platelets, you have to do a differential diagnosis to do that breakdown. That follows through medications. We all know the famotidine issue for many years, or PPIs [proton pump inhibitors], can cause thrombocytopenia. The VA [Veterans Affairs] is notorious for it. Another area is infection. We know that hepatitis C causes thrombocytopenia, as does AIDS, and even chickenpox, which actually addresses that antibody response, that cross-reactivity.
Then you follow through with other areas. As you mentioned, lupus, rheumatoid arthritis, pregnancy, and patient populations with lymphoma have normal antibody development against platelet proteins that can cause thrombocytopenia. In some cases, it’s just unknown—idiopathic, which is the correct definition of the idiot: unknown diagnosis. Those added root causes being differentiated for that pathophysiology allows us to define what’s causing the thrombocytopenia and what that diagnosis is. From there, we can potentiate from the pathophysiology of ITP what those treatments are for those low platelets in the case for ITP diagnosis.
Bhavesh Shah, RPh, BCOP: Wow, there’s a lot of exclusions that you have to do before you can actually give a patient a diagnosis. It’s not straightforward. It’s not as if you can do a bone marrow biopsy and voilà, you have ITP. There are a lot of exclusions, as you both mentioned.