Background: Schnitzler's syndrome is a rare disorder characterized by chronic urticaria and monoclonal IgM gammopathy. The mechanisms of the urticarial flares remain poorly understood.
Objective: To more accurately define the histopathologic changes in urticarial lesions, we reviewed 25 original biopsies from 15 cases of Schnitzler's syndrome, 11 of which have previously been reported.
Results: Thirteen specimens from 9 patients showed urticaria with neutrophils (neutrophilic urticaria). Necrotizing leukocytoclastic vasculitis with positive immunofluorescence studies was found only in 2 biopsies from 1 patient who was genetically deficient in C4. Five specimens showed lymphocytic urticaria. Four biopsies demonstrated a spongiotic dermatitis; an eosinophilic spongiosis was seen in 2 biopsies from a patient who later developed pemphigus vulgaris. Epidermal changes were seen in 17 specimens from 10 patients.
Conclusions: The histopathologic findings in Schnitzler's syndrome are not uniform although most cases demonstrated neutrophilic urticaria. Neutrophils in Schnitzler's syndrome are not usually related to immune complex vasculitis. Epidermal changes in Schnitzler's syndrome need to be further analyzed.