A child with severe systemic mastocytosis (SM) remained unresponsive to conventional medical treatments until the initiation of omalizumab rapidly led to a complete and steady resolution of all symptoms, according to a new case report published in the Italian Journal of Pediatrics.

The study authors reported on a case of an 8-year-old Caucasian male patient who was referred to the clinic after an episode of anaphylaxis of unknown origin, marked by persistent high tryptase value and symptoms of hypotension, tachycardia, and general flushing, but no urticaria or angioedema.

Past medical records pointed out a diagnosis of urticaria pigmentosa as well as rare occurrences of flushing, gastrointestinal discomfort, and bronchospasm. However, the physical exam was normal upon presentation.

The patient underwent extensive diagnostic testing including bone marrow biopsy, chest radiography, abdominal ultrasound, and a bone density scan that confirmed the evolution of his condition toward indolent SM.

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He was treated unsuccessfully with high doses of oral nonsedating antihistamines, cromolyn sodium, topical steroids, and oral steroids. Over time, the patient experienced frequent disease flares marked by recurrent flushing, diarrhea, abdominal pain, palpitations, musculoskeletal symptoms, and fatigue.

A year later, the patient was started on omalizumab every 4 weeks subcutaneously and the previous therapy plan remained unchanged. Omalizumab treatment resulted in a complete withdrawal of symptoms after only the second dose and the medication was well tolerated, with no side effects except for minimal local swelling, the authors wrote.

Laboratory testing showed that serum tryptase levels remained stable, while total immunoglobulin E (IgE) levels escalated after the first dose of omalizumab and remained steadily increased.

Twenty months after the initiation of omalizumab, the patient remained free of symptoms and other anaphylactic episodes. Steroid therapy was discontinued and the use of antihistamines was steadily reduced.

“When, due to the COVID-19 quarantine, a dose of omalizumab was missed, after 6 weeks after the last treatment, the patient returned to be symptomatic (flushing, headache, diarrhea) and steroid-dependent. Short after the reintroduction of omalizumab therapy, the symptoms completely disappeared and, since then, steroids could be permanently discontinued,” Bossi and colleagues noted.

Omalizumab is a recombinant humanized murine monoclonal anti-IgE antibody that can reversibly bind to the free serum IgE and prevent it from binding to its high-affinity receptor on the surface of mast cells and basophils. This way, the medication not only reduces the concentration of free IgE in the serum but also downregulates the mast cells and their ability to release mediators.

Reference

Bossi G, Brazzelli V, De Amici M, et al. Successful treatment with omalizumab of a child affected by systemic mastocytosis: clinical and biological implications. Ital J Pediatr. Published online January 13, 2023. doi:10.1186/s13052-022-01402-7