The growing number of children with rare diseases such as cutaneous mastocytoma and juvenile xanthogranuloma turning to dermatologists, as well as their clinical similarity, dictate the need for specialists to pay careful attention to these diseases. cutaneous mastocytoma is a clinical form of cutaneous mastocytosis. According to the WHO classification (2022), isolated (one focus) and multiple cutaneous mastocytoma (no more than three foci) are distinguished. juvenile xanthogranuloma belongs to the group of non-Langerhans cell histiocytosis, a broad group of related diseases characterized by the proliferation of histiocytes other than Langerhans cells. We describe a case of an unusual clinical course of solitary juvenile xanthogranuloma in a 3-year-old boy referred to Moscow Scientific and Practical Center of Dermatovenereology and Cosmetology with suspected cutaneous mastocytoma. The size, unusual shape, localization of the lesion and elevated levels of serum tryptase exceeding the age norm (<5 μg/l) determined the atypicality of this case. Dermoscopic examination revealed a central deep yellow coloration of the lesion in the center (the setting sun symptom), a vascular pattern and a clouds symptom. Pathological examination confirmed the diagnosis of juvenile xanthogranuloma. The article also reflects the results of a dynamic observation of a child with an isolated large-sized cutaneous mastocytoma. During the examination, an increase in tryptase levels (>20 μg/l), and AST values, as well as ultrasound signs of hepatomegaly were revealed. Features of the dermoscopic and pathomorphological picture demonstrated patterns characteristic of infiltration and increased activity of mast cells. Cutaneous mastocytoma and juvenile xanthogranuloma are rare and benign skin diseases that usually begin in childhood. Diagnosis of rare diseases often requires complex differential diagnosis. Features of the modern course of cutaneous mastocytoma and juvenile xanthogranuloma are an atypical clinical picture and a high risk of developing extracutaneous symptoms. The presented clinical cases demonstrate the need for interdisciplinary monitoring of patients with these diseases and change the stereotypes of treating them as independent and regressive processes without a trace.
