Mastocytosis is a group of rare heterogeneous diseases caused by excessive proliferation and accumulation of mast cells in various organs and systems. Diagnosis of mastocytosis with gastrointestinal tract involvement is a difficult task, since the symptoms often resemble other, more common diseases.

The aim of the study is to describe the problems of diagnosing systemic mastocytosis with gastrointestinal involvement based on a clinical case.

Materials and methods. The clinical observation of a 57-year-old patient who complained of periodic flatulence, diarrhea, discomfort in the left iliac region, weight loss, periodic manifestations of mild depression is presented.

Results. Endoscopic examination of the colon revealed multiple whitish plaque-like formations of unclear origin, not pathognomonic for other diseases of the colon. Histological and immunohistochemical studies of colon biopsies revealed the major and minor criteria that allowed the diagnosis of systemic mastocytosis with gastrointestinal involvement. An elevated serum tryptase level further supported the diagnosis of systemic mastocytosis in this patient.

Conclusions. Systemic mastocytosis with gastrointestinal involvement is difficult to diagnose, significantly impairs patients’ quality of life, and some of its forms can be life-threatening as they progress, therefore requiring careful clinical follow-up and laboratory monitoring. Qualified medical care for patients with systemic mastocytosis, including those with gastrointestinal involvement, requires a multidisciplinary team of specialists with the participation of a gastroenterologist, endoscopist, hematologist, and pathologist. Early and timely diagnosis of systemic mastocytosis is important not only for the symptom control, but also for slowing the progression of the disease.