Familial urticaria pigmentosa with giant mast cell granules. A clinical, light, and electron microscopic study

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Abstract
Urticaria pigmentosa (UP) developed in 2 sisters in infancy. The lesions in both patients contained an extensive infiltration of large, tightly packed mast cells. The number of mast cells and the histamine content were increased in the lesions of both patients and also in the clinically normal skin of 1 subject. A proportion of mast cells in lesional and perilesional skin was found, by light microscopy, to contain giant cytoplasmic granules that on EM were noted to reach a maximum size of .apprx. 6 .mu.m in diameter and to have an abnormal ultrastrucutre. Giant granules were not seen in other cell types, including neutrophils and melanocytes. Apparently, genetic factors are important in determining this variant of UP, and the disease may be more widespread in the skin than the eruption indicates.