Abstract
Eosinophilia may result from three main causes: secondary (reactive), primary (clonal), and/or idiopathic. The diagnosis of idiopathic eosinophilia must be made based on excluding all reactive or clonal causes. However, some causes may be very rare so as to be misdiagnosed as idiopathic. We present the case of eosinophilia caused by aggressive systemic mastocytosis, originally recognized as idiopathic. Lymphadenopathy, dysmyelopoiesis, and hepatosplenomegaly gradually appeared and deteriorated with increasing eosinophils. This case carried KIT D816V mutation. The BCR::ABL fusion gene and the mutations in JAK2 V617F, PDGFRα, and PDGFRβ in bone marrow were all negative. PHF6, PPM1D, and TET2 mutations were demonstrable. The patient was prescribed to avapritinib. The condition was effectively controlled. However, the patient discontinued medication for economic reasons 5 months later. Disease progression happened and died 10 months after diagnosis. Our study indicates that gene mutation detection at diagnosis is helpful for patient accurate diagnosis and targeted therapy of such patients.