INDOLENT SYSTEMIC MASTOCYTOSIS PRESENTING AS AN EXCIPIENT ALLERGY

Abstract

<h3>Introduction</h3> Systemic mastocytosis may present with anaphylaxis to unrelated medications. Here we present a case of suspected macrogol excipient allergy which was found to be due to indolent systemic mastocytosis (ISM). <h3>Case Description</h3> 43 yo woman with history of ulcerative colitis presented for evaluation of anaphylaxis to infliximab, vedolizumab, and possibly the influenza vaccine over the last year. Prior to this she had no known medication allergies. Within minutes of receiving both monoclonal antibodies she developed flushing, hypotension, lightheadedness, and in one case syncope. Her symptoms resolved with rapidly administered epinephrine, methylprednisolone, and intravenous fluids. Infliximab, vedolizumab, and the flu vaccine each contain polysorbate 80 suggesting an IgE mediated macrogol allergy. Interestingly, she tolerated other medications containing polysorbate 80 (sertraline and bupropion) and polyethylene glycol (methylprednisolone and previously a bowel prep). Macrogol skin prick and intradermal testing were completely negative. Further investigation revealed elevated baseline tryptase (13.1 ng/mL), negative testing for hereditary alpha tryptasemia, and elevated urine methyl histamine (265 mcg/g Cr) and prostaglandin D2 (3360 pg/mg Cr) metabolites. The D816V KIT mutation was present in peripheral blood suggesting ISM. Given that she lacked frequent symptoms and had no evidence of end organ dysfunction, the patient deferred bone marrow biopsy to confirm the diagnosis. <h3>Discussion</h3> In this patient with anaphylaxis to multiple medications and negative skin testing, elevated tryptase suggested an underlying mast cell disorder. KIT mutation D816V is detectable peripherally in the vast majority of SM and can help make a probable diagnosis in patients with indolent disease wishing to avoid bone marrow biopsy.