Systemic mastocytosis involves the bone marrow in the majority of cases and in some cases other internal organs, usually in addition to involving the skin. Mast cells collect in various tissues and can affect organs where mast cells do not normally inhabit such as the liver, spleen and lymph nodes, and organs which have normal populations but where numbers are increased. In the bowel, it may manifest as mastocytic enterocolitis.[15] However, normal ranges for mast cell counts in the gastrointestinal tract mucosa are not well established in the literature, and depend upon the exact location (e.g. right versus left colon), gender, and patient populations (such as asymptomatic patients versus patients with chronic diarrhea of unknown etiology). Quantitative mast cell stains may yield little diagnostic information, and further research studies are warranted to determine whether "mastocytic enterocolitis" truly represents a distinct entity.

Reference
Wiki: Systemic mastocytosis