The interstitial variant of granuloma annulare: Clinicopathologic study of 69 cases with a comparison with conventional granuloma annulare

BACKGROUND: The full-blown lesion of granuloma annulare (GA) is characterized by necrobiotic granulomas with palisading of histiocytes and stromal mucin deposition. Cases in which the granulomatous features are not fully developed have been described as the "interstitial" variant; however, there is no good definition regarding their criteria for diagnosis. METHODS: We conducted a retrospective study of 97 cases of GA. RESULTS: Cases of interstitial GA (69) were paucicellular with scant to no mucin, with only a few scattered mononuclear cells but lacking well-formed granulomas with multinucleated giant cells. Immunohistochemical study showed that the cells in conventional cases of GA stained strongly positive for CD68 and CD163, whereas the small mononuclear cells in interstitial GA were strongly positive only for CD163. CONCLUSIONS: Interstitial GA differs from the classical GA in several respects, including morphology and immunophenotype. Use of antibodies to CD163 may be helpful for distinguishing the interstitial variant from other conditions. Recognition of the interstitial variant is of importance to explain the presence of lesions that clinically are suspicious for GA but histologically do not resemble the conventional form of the disease.