Diffuse cutaneous mastocytosis (DCM) is the rarest and most severe clinical form of mastocytosis in children. The frequency of DCM among forms of skin mastocytosis varies from 1 to 13%. Major spontaneous vesicles formation is the leading clinical sign of disease in neonatal and infant periods. Rubbing or scratching of skin lesions during DCM causes immediate release of mast cell mediators and leads to flushing reactions, urticaria, up to the development of anaphylactic shock and death. The clinical case of DCM in a 3 months old boy with multiple vesicular rashes, yellow-brown infiltrated plaques and areas of atrophy on the scalp, face, body, upper and lower limbs is presented. In the morphological study of skin bioptate, pigmentation of the basal epidermis layer’s keratinocytes without signs of pigment deposition, massive infiltration of the upper dermis layer by lymphomonocyte subpopulations and separation with the formation of subepidermal vesicle were determined. The positive reaction was shown in immunohistochemical staining with antibodies to CD117. Reaction with antibodies to Melan A, S100 and Langerin was negative. Immunohistochemical examination in the observed patient allowed to eliminate hematological diseases and cancer. The blood serum tryptase level was 14.2 μg/l (normal value is less than 11 μg/l). During the dermatoscopic rash examination a vesicle of yellow-brown color and with rounded outlines was visualized in the focus center. Intense yellow coloring with linear vascular structures was on its periphery. Clinical diagnostics of DCM requires comprehensive differential diagnosis and interdisciplinary interaction. For this reason, the focus is on the results of pathomorphological and immunohistochemical examinations of bioptate. Parents should be informed about the serious complications that may develop from the massive release of mast cell mediators. Follow-up of patients with DCM requires dermatologist’s follow-up, monitoring of the state of internal organs’ functions, hematological indicators and tryptase level.
