Should we perform bone marrow biopsy in patients with hypereosinophilia of unknown etiology?

Florence Roufosse, MD, is a professor of medicine, internist, and clinical immunologist at the Erasmus University Hospital in Brussels, Belgium. She has served as president of the International Eosinophil Society. She is involved in clinical trials investigating hypereosinophilic syndrome.

Should we perform bone marrow biopsy in patients with hypereosinophilia of unknown etiology without features of a myeloproliferative neoplasm?

There are very, very clear guidelines about when to do bone marrow biopsy. For sure, we don’t biopsy all our patients with hypereosinophilia that is unexplained. It depends a bit on the clinical profile. And there are actually lots of things that can be found in peripheral blood. Even if you have a patient who has a clonal eosinophilic disorder, which is mediated by the fusion gene FIP1L1-PDGFRA, you can actually demonstrate that site of genetic rearrangement on peripheral blood.

That being said, if you have features of myeloproliferative disease, yes, you have to perform bone marrow biopsy. Other patients who we would tend to biopsy is if you have elevated serum tryptase, because mast cell disorders can be accompanied by hypereosinophilia; patients who have T-cell abnormalities as well: if you have an abnormal phenotype, this can be a lymphoid variant of hypereosinophilic syndrome, which is a benign disorder, but it also could be T-cell lymphoma, so you have to biopsy these patients.

The recommendations, I’d say, are you biopsy patients in whom you have serum biomarkers of myeloproliferative disease like elevated vitamin B₁₂, elevated tryptase, abnormal T-cell flow or clonal T-cell receptor (TCR) gene rearrangement patterns. Some people also tend to biopsy patients when their blood eosinophil count is >5000/microL—it’s kind of arbitrary, but those are the types of situations where you would bone marrow biopsy a patient. It’s important to know that myeloproliferative disease forms can eventually really take clinical expression of an idiopathic hypereosinophilic syndrome, so at some point you have to consider the patient may have clonal eosinophilia.