Lung diseases associated with digital clubbing

Clubbing is classified into conditions in which it is commonly, occasionally, rarely and never observed. Hypertrophic osteoarthropathy may be a more extreme form of clubbing, but is more likely to be a related but nevertheless qualitatively different phenomenon. Megakaryocytes or platelet clumps impacting in a digital stratum are plausible causes of clubbing, through the local release of platelet-derived growth factor (PDGF).