Pseudolymphomatous Granuloma Annulare Rich in B Lymphocytes

Granuloma annulare is a non-infectious granulomatous dermatosis with a probable pathogenic mechanism of delayed-type hypersensitivity, in which the dermal histiocytic granulomatous infiltrate is usually accompanied by a lesser component of lymphocytes. Although there are more common clinical and histopathological patterns of presentation, there are less well-known variants that may pose significant diagnostic challenges by mimicking other inflammatory cutaneous processes or even neoplastic conditions. One of the rarest forms of granuloma annulare is the pseudolymphomatous variant, in which the lymphocytic component is not only highly prominent but may, in some cases, partially or completely obscure the histiocytic component itself. This feature, together with the fact that the clinical presentation of this variant is often atypical-frequently lacking the characteristic annular morphology of conventional granuloma annulare-renders the diagnosis particularly challenging. From an immunohistochemical standpoint, the infiltrates described are predominantly composed of T cells, with only a sparse and scattered B-cell component. In this article, we present a case of granuloma annulare with a pseudolymphomatous B-cell component (PAX5⁺, CD79⁺) and minimal T-cell involvement, observed in a 4 mm skin nodule located on the shoulder of a 48-year-old male. This case therefore broadens the concept of pseudolymphomatous granuloma annulare to include infiltrates predominantly composed of B lymphocytes.