To investigate ultrastructural characteristics of mast cells in urticaria pigmentosa in comparison to mast cells in other conditions and to search for the possible differences of ultrastuctural features amog different types of urticaria pigmentosa as well as those from normal mast cells, 4 cases of urticaria pigmentosa and 1 case of mastocytosis associated with capillary hemangioma were studied by both light and electron microscopic examinations. The cases of urticaria pigmentosa consisted of one case of blister type from a 3 month old ma1e infant, 2 cases of maculo-papular type both from 10 month old male infants, and a case of nodular type from a 14 month old boy. Ultrastructural features of mast cells in urticaria pigmentosa, in general; a) appeared relatively immature; b) mast cells in nodular type of urticaria pigmentosa were mostly round shaped while other types showed spindle or oblong shapes; c) mast cells in the maculo-papular type and those in hemangioma were similar and resembled normal mast cells; and d) marked degranulation of mast cells in the form of expulsion of granules, perigranular vacuole formation and intracellular disolution of granules for the blister type of urticaria pigmentosa.
Adolescent ; Cytoplasmic Granules/ultrastructure ; Human ; Male ; Mast Cells/ultrastructure ; Microscopy, Electron ; Urticaria Pigmentosa/pathology*