Electron microscopic findings in a case of systemic mastocytosis.

For several decades urticaria pigmentosa had been considered to be a benign and purely cutaneous disease, caused by infiltrations of tissue mast cells in the skin. Yet until 1962 at least 24 cases of systemic mastocytosis had been published. Sagher estimated the incidence of systemic mastocytosis as being in the region of about 10% of all cases of urticaria pigmentosa. A case of systemic mastocytosis in a 4-year-old child is described. Biopsy specimens were examined by electron microscopy to study the process of degranulation of tissue mast cells during which histamine and heparin are released.