D1.416 - Pediatric Mast Cell Activation Syndrome: A Case Series Highlighting Varied Clinical Responses to Treatment and natural history

Mast Cell Activation Syndrome (MCAS) is a rare and often underdiagnosed condition, characterized by episodic symptoms resulting from spontaneous inappropriate mast cell activation and degranulation. Despite increasing recognition in adults, pediatric literature remain limited, and guidelines for diagnosis and management of MCAS in children are lacking.

We present here the diagnosis, treatment and natural history of a case series of three children with MCAS.

All children were diagnosed according to adult accepted criteria including recurrent episodes of idiopathic anaphylaxis. Anaphylaxis was documented clinically, responded well to anti allergic medication and was supported by a pathologic Tryptase transient elevation. In all cases no possible external trigger was recognized.

The first two cases were both 5 years old upon diagnosis, and were successfully managed with regular high-dose antihistamines (AH), resulting in marked symptom improvement. Both patients achieved extended asymptomatic intervals, during which treatment was gradually tapered down when possible and eventually discontinued. The first patient stopped treatment after 4 years and is now asymptomatic for 18 months, and the second patients stopped treatment after 5 years, and had no relapse for 6 months now.

The third patient was 11 years old when diagnosed, and experienced persistent attacks despite high-dose regular AH treatment. Given the lack of adequate response to AH, this patient was initiated on Omalizumab 300mg once a month, which has been shown to be effective in treating mast cell-related disorders in adults. This additional therapy led to significant symptom improvement and the patient is symptoms free for three years now.  

These cases demonstrate the potential for long-term symptom control with AH therapy, but also highlighting the need for personalized treatment approaches in pediatric MCAS. We also suggest that some pediatric patients may experience a self-limited course of the disease, a unique feature of MCAS that has not been described to date. While current guidelines provide a framework for diagnosis, the variability in diagnosis and treatment response among pediatric patients is still under-studied. This emphasizes the need for ongoing research to better understand the pathophysiology and optimize therapeutic strategies for this complex and under recognized disorder in the pediatric population.