Researchers presented the case study of a patient who was diagnosed with indolent systemic mastocytosis after initially presenting as a case of excipient allergy, according to a study published in the Annals of Allergy, Asthma & Immunology.

A 43-year-old woman presented with signs of anaphylaxis, thought to be secondary to infliximab, vedolizumab, and the influenza vaccine. She had a history of ulcerative colitis but no known drug allergies. 

When the patient was administered monoclonal antibodies, she instantly developed flushing, hypotension, and lightheadedness. On one occasion, she developed syncope. Nevertheless, these symptoms rapidly resolved with the administration of intravenous fluids, epinephrine, and methylprednisolone. 

Read more about systemic mastocytosis etiology 

When assessing the possible causes of her anaphylaxis-like manifestations, her physicians considered that infliximab, vedolizumab, and the influenza vaccine each contained polysorbate 80. This is a possible cause of immunoglobulin E-mediated macrogol allergy. However, the patient appeared to tolerate other medications containing polysorbate 80, such as sertraline and bupropion, as well as those containing polyethylene glycol, such as methylprednisolone. 

Her physicians proceeded to conduct a macrogol skin prick and intradermal test, which returned negative. Further laboratory investigations revealed elevated baseline levels of tryptase at 13.1 ng/mL, urine methyl histamine at 265 mcg/g Cr, and prostaglandin D2 metabolites at 3360 pg/mg Cr. The patient tested negative for hereditary alpha tryptasemia. 

Crucially, the patient’s physicians discovered that the D816V KIT mutation was present in her peripheral blood, which was indicative of indolent systemic mastocytosis. Because the patient lacked frequent symptoms and did not demonstrate evidence of end organ damage, she decided to defer bone marrow biopsy for further confirmation of the diagnosis. 

“Systemic mastocytosis may present with anaphylaxis to unrelated medications,” the authors of the study wrote. “KIT mutation D816V is detectable peripherally in the vast majority of [systemic mastocytosis] and can help make a probable diagnosis in patients with indolent disease wishing to avoid bone marrow biopsy.”


Franzblau L, Khan D. Indolent systemic mastocytosis presenting as an excipient allergy. Ann Allergy Asthma Immunol. 2022;129(5):S96. doi:10.1016/j.anai.2022.08.772