MITOTIC GRANULOMA-ANNULARE - A CLINICOPATHOLOGICAL STUDY OF 20 CASES

The finding of mitotic figures in granuloma annulare (GA) has not been emphasized in the literature. We describe 20 cases of a cellular, mit otically active variant of GA; we defined this group as cases having g reater than or equal to 1 mitosis per 10 hpf. Clinically, the lesions could not be distinguished from typical, localized GA: there were 9 ma les and 11 females with a mean patient age of 49+/-15 years (mean+/-SD ), compared to 45+/-20 years in a randomly selected control group of 6 0 patients with GA, and no unusual sites of predilection were noted. H istologically, a classic, palisading granuloma pattern predominated (1 8/20 cases). Lesions were located in the mid-dermis and tended to be m ore cellular than typical GA. The histiocytes comprising the lesion of ten had enlarged nuclei and prominent nucleoli. The number of mitoses per 10 hpf was 3.0+/-1.5 (range 1.0-7.2), control group 0.3+/-0.5; occ asional atypical mitotic figures were observed. The proliferative natu re of these lesions was confirmed using MIB-1 staining; the percentage of MIB-1 positive cells ranged from 5%-29% (mean 15+/-6%). Mitotic GA must be distinguished histologically from neoplastic processes, in pa rticular epithelioid sarcoma. We conclude that histiocytes in clinical ly typical GA can exhibit an increased mitotic rate. Recognition of th is variant is important in order to avoid overdiagnosis of a malignant condition. (C) Munksgaard 1996.