Interstitial granulomatous dermatitis without arthritis: successful therapy with hydroxychloroquine

Interstitial granulomatous dermatitis is a rare entity characterized by cutaneous linear strands (the "rope sign") and rheumatoid arthritis. In the past years, 12 other cases have been described with variable cutaneous symptoms. All showed similar histological features, resembling those of granuloma annulare or 'palisaded neutrophilic and granulomatous dermatitis', suggesting a wide spectrum for a single entity. A 60-year-old patient presented with erythematous patches with an indurated, violaceous border resembling the "rope sign" on both flanks. The histological investigation revealed dense diffuse interstitial inflammatory infiltrates composed of eosinophils, neutrophils, lymphocytes, macrophages and multinucleated giant cells in the superficial and deep dermis. In the deep dermis, prominent eosinophilic degenerated collagen fibres with surrounding macrophages ('floating sign') occurred. In contrast to most previously described patients, our patient did not have arthralgias. The skin findings cleared following therapy with hydroxychloroquine.