Confirmed Systemic Mastocytosis in a Pediatric Patient With Widespread Cutaneous Symptoms

Mastocytosis is characterized by the clonal expansion of mast cells, with deposition into various organs and variable clinical presentation depending on subtype. It generally results from a mutation in the KIT gene, which encodes for production of receptor tyrosine kinases, the constitutive activity of which results in abnormal cell growth and proliferation. In pediatric patients, the cutaneous mastocytosis (CM) form predominates, and systemic mastocytosis (SM) is rarely reported. Accordingly, clinical course and management are not well described. We describe a case of SM in a 10-year-old child who was initially suspected of having widespread CM. The child had initially minimal systemic symptoms that are usually described in SM. Peripheral testing for the most common KIT mutation associated with constitutive activity, c-KIT D816V, in which aspartic acid is substituted for valine at position 816, was negative. Rising serum tryptase and increasing systemic symptoms of histamine release led to bone marrow biopsy, which was positive for the c-KIT D816V mutation and confirmed the diagnosis of indolent SM. The patient's response to treatment is briefly described, with exploration of treatment modalities described in previously reported cases. The case illustrates that, even in the absence of classic systemic symptoms, an index of suspicion for SM should be maintained, and highlights that peripheral testing for the c-KIT D816V mutation may be represent a false negative. Finally, we discuss that although antihistamines have historically formed the backbone of treatment in pediatric SM, the increasing availability of biological agents present possible new treatments with some success reported in the literature.