2.18 Digital Clubbing

Pulmonary system review for the USMLE Step 1 Exam

• Digital clubbing is the enlargement of the ends of fingers and toes due to growth of connective tissue between the nail matrix and the distal portion of the digit.
• It is defined quantitatively as an increased angle between nail bed and nail plate (> 180°).
• Digital clubbing is caused by an interaction between platelets, megakaryocytes, and the growth factors platelet derived growth factor (PDGF) and vascular endothelial growth factors (VEGF).
• Diseases associated with digital clubbing include lung cancer, cystic fibrosis, idiopathic pulmonary fibrosis, bronchiectasis, and an empyema.
• Digital clubbing is usually not associated with asthma or COPD.