Microscopic morphology of different types of urticaria

To identify possible special histopathologic features of different types of urticaria.

Hematoxylin-eosin- and toluidine blue-stained sections from biopsy specimens of all patients with urticaria seen from 1990 to 1993.

Inpatient and outpatient services of the Virchow Klinikum, Humboldt University, Berlin, Germany.

We studied spontaneous or induced wheals of 108 patients with acute, chronic, and physical urticaria who consented to an additional biopsy from uninvolved skin. The controls were 10 normal volunteers with wheals that tested positive on a prick test and who had contralateral normal skin.

Mast cell numbers in both lesional and nonlesional skin in the upper and lower dermis of biopsy specimens from patients and controls.

Blind evaluations of microscopic sections showed dermal edema and dilated lymphatic and vascular (P < .001 for all, Fisher exact test) capillaries almost exclusively in involved skin. The same held for inflammatory infiltrates, with significantly increased numbers of neutrophils and eosinophils in specimens from patients with acute urticaria and those with delayed pressure urticaria (P < .01 for each). Mast cell numbers were higher in the upper (P < .01) and lower dermis (P < .05) of lesional and uninvolved skin of all patients with urticaria, with a further increase (P < .01) in patients with disease of more than 10 weeks' duration. Edema and vascular changes were most prominent in the skin of patients with cold urticaria (P < .005) and mononuclear infiltrates were more pronounced in those with cold urticaria, chronic urticaria, and prick test-positive wheals (P < .05 for each) and in the lower dermis of patients with delayed pressure urticaria (P < .001).

In all types of urticaria, mechanisms must be operative that cause an increase of cutaneous mast cells. Distinctive pathological features can be identified in different types of urticaria, although these are not diagnostic.