Expansion
Respiratory, cardiac, gastrointestinal and endocrine causes
Expansion
Respiratory (the largest group)
- Lung carcinoma, mesothelioma
- Suppurative disease: bronchiectasis, cystic fibrosis, empyema, lung abscess
- Fibrosis: idiopathic pulmonary fibrosis, asbestosis
- Not COPD or asthma
Cardiac
- Cyanotic congenital heart disease
- Infective endocarditis
- Atrial myxoma
Gastrointestinal
- Inflammatory bowel disease
- Cirrhosis, especially primary biliary cholangitis
- Coeliac disease
Other
- Thyroid acropachy in Graves disease
- Familial and idiopathic
The crucial negative is that COPD does not cause clubbing. Since most patients with COPD are smokers, finding clubbing in that population points towards bronchial carcinoma, bronchiectasis or fibrosis, and warrants investigation rather than being attributed to the known lung disease.
Unilateral clubbing suggests a local vascular cause such as an axillary or subclavian aneurysm or an arteriovenous fistula.
The mechanism is thought to involve megakaryocytes bypassing the pulmonary capillary bed and releasing platelet-derived growth factor in the digits.