A clinical and histological study of urticaria pigmentosa: relationships between mast cell proliferation and the clinical and histological manifestations.

In 21 cases of urticaria pigmentosa (UP), clinical and histological observations and evaluation of mast cell (MC) volume density in the lesions using a morphometric point counting method were performed. The mutual correlations between clinical and histological findings were statistically assessed by a method of multiple regression analysis. Clinical items employed in the analyses were as follows: sex, the age of onset, the age of biopsy, the biopsy, the duration of lesions, the type of skin lesions, sites involved, the presence or absence of Darier's sign of Darier's sign and symptoms, and serum histamine level. Histological items included the localization and infiltration pattern of MC, the level of basal melanosis, the presence or absence of inflammatory cell infiltration, and the MC volume density in the lesions. Statistical significance of the partial regression coefficients was obtained for 6 pairs of the criteria (p = 0.05), including the age of onset and the age of biopsy, the age of onset and the level of basal melanosis, the duration of lesions and the level of basal melanosis, and the type of skin lesions and the level of basal melanosis. No significant correlations were observed between the MC volume density in the lesions and any of the other items. These results suggest that the basal melanosis in a UP lesion may not be a direct reaction to the transitory massive infiltration of MC, but rather be due to a relatively long-term effect of MC infiltration. Furthermore, the MC volume density in the lesion is not likely to be an important factor in determining the clinical manifestations of a UP lesion.