Why Do Rheumatic Diseases with Pulmonary Fibrosis Rarely Develop Digital Clubbing?

Digital clubbing, or hypertrophic osteoarthropathy in its more advanced form, is a distinctive clinical sign characterized by bulbous enlargement of the distal phalanges and increased nail curvature. It is classically associated with neoplastic, infectious, and hepatopulmonary diseases, where tissue hypoxia and circulating angiogenic mediators play central roles. In contrast, rheumatic diseases such as rheumatoid arthritis, systemic sclerosis, and idiopathic inflammatory myopathies, even when complicated by significant pulmonary fibrosis and hypoxemia, rarely present with digital clubbing. This review explores the pathophysiologic mechanisms of clubbing, contrasts them with the pathogenesis of rheumatic interstitial lung disease (ILD), and discusses why autoimmune fibrotic processes may inherently prevent the development of this ancient clinical sign. The rarity of clubbing in autoimmune ILD has diagnostic and pathogenetic implications that extend beyond clinical observation, suggesting fundamental differences in vascular and cytokine regulation compared with neoplastic or infectious fibrosis.