Rheumatoid arthritis (RA) is an idiopathic arthropathy syndrome that has a propensity to affect the small joints of the hands and feet with extra-articular manifestations comprising skin lesions, neuropathy, pericarditis, pleuritis, interstitial pulmonary fibrosis and a systemic polyarteritis nodosa (PAN)-like vasculitic syndrome. The most widely recognized skin lesion is the rheumatoid nodule. Other skin manifestations are poorly defined.
Using a natural language search of the authors' outpatient dermatopathology databases, skin biopsies from 43 patients with RA were selected for retrospective analysis in an attempt to define the dermatopathological spectrum of RA and its clinical correlates.
The biopsies were categorized by the dominant histologic pattern, recognizing that in most cases there were additional minor reaction patterns. Palisading and/or diffuse interstitial granulomatous inflammation was the dominant pattern seen in 21 patients; the lesions included nodules, plaques and papules with a predilection to involve skin over joints. Besides interstitial histiocytic infiltrates and variable collagen necrobiosis, these cases also showed interstitial neutrophilia, vasculitis and pauci-inflammatory vascular thrombosis. The dominant morphology in 11 other patients was vasculopathic in nature: pauci-inflammatory vascular thrombosis, glomeruloid neovascularization, a neutrophilic vasculitis of pustular, folliculocentric, leukocytoclastic or benign cutaneous PAN types, granulomatous vasculitis, and lymphocytic vasculitis and finally occlusive intravascular histiocytic foci for which the designation of "RA-associated intravascular histiocytopathy" is proposed. Rheumatoid factor (RF) positivity and active arthritis were common in this group, with anti-Ro and anticardiolipin antibodies being co-factors contributing to vascular injury in some cases. Immunofluorescent testing in three patients revealed dominant vascular IgA deposition. In nine patients, the main pattern was one of neutrophilic dermal and/or subcuticular infiltrates manifested clinically as urticarial plaques, pyoderma gangrenosum and panniculitis.
The cutaneous manifestations of RA are varied and encompass a number of entities, some of which define the dominant clinical features, such as the rheumatoid papule or subcutaneous cords, while others allude to the histopathology, i.e. rheumatoid neutrophilic dermatosis. We propose a more simplified classification scheme using the adjectival modifiers of "rheumatoid-associated" and then further categorizing the lesion according to the dominant reaction pattern. Three principal reaction patterns are recognized, namely extravascular palisading granulomatous inflammation, interstitial and/or subcuticular neutrophilia and active vasculopathy encompassing lymphocyte-dominant, neutrophil-rich and granulomatous vasculitis. In most cases, an overlap of the three reaction patterns is seen. Co-factors for the vascular injury that we believe are integral to the skin lesions of RA include RF, anti-endothelial antibodies of IgA class, anti-Ro and anticardiolipin antibodies.