Clubbing: an update on diagnosis, differential diagnosis, pathophysiology, and clinical relevance.

Finger clubbing can be a striking physical finding. At other times, the presence of clubbing is difficult to establish by subjective examination alone and the profile angle or distal phalangeal to interphalangeal depth ratio are needed to confirm the finding. Most microscopic and imaging studies of clubbed fingers reveal hypervascularization of the distal digits. Recent research shows that when platelet precursors fail to become fragmented into platelets within the pulmonary circulation, they are easily trapped in the peripheral vasculature, releasing platelet-derived growth factor and vascular endothelial growth factor, promoters of vascularity and, ultimately, clubbing. Clinically, clubbing is associated with a number of neoplastic, pulmonary, cardiac, gastrointestinal, infectious, endocrine, psychiatric, and multisystem diseases. In narrowing the differential diagnosis, we recommend a detailed history and physical examination accompanied by focused laboratory and imaging studies. An algorithm for the evaluation of newly diagnosed clubbing is suggested.