Nail clubbing, also known as digital clubbing or clubbing, is a deformity of the finger or toe nails associated with a number of diseases, mostly of the heart and lungs. When it occurs together with joint effusions, joint pains, and abnormal skin and bone growth it is known as hypertrophic osteoarthropathy.Clubbing is associated with lung cancer, lung infections, interstitial lung disease, cystic fibrosis, or cardiovascular disease. Clubbing may also run in families, and occur unassociated with other medical problems.The incidence of clubbing is unknown; it was present in about 1% of people admitted to an internal medicine unit of a hospital. Clubbing has been recognized as a sign of disease since the time of Hippocrates. Causes
Clubbing is associated with

Lung disease:
Lung cancer
Interstitial lung disease most commonly idiopathic pulmonary fibrosis
Complicated tuberculosis
Suppurative lung disease: lung abscess, empyema, bronchiectasis, cystic fibrosis
Mesothelioma of the pleura
Arteriovenous fistula or malformation
Sarcoidosis
Heart disease:
Any disease featuring chronic hypoxia
Congenital cyanotic heart disease (most common cardiac cause)
Subacute bacterial endocarditis
Atrial myxoma (benign tumor)
Tetralogy of Fallot
Gastrointestinal and hepatobiliary:
Malabsorption
Crohns disease and ulcerative colitis
Cirrhosis, especially in primary biliary cholangitis
Hepatopulmonary syndrome, a complication of cirrhosis
Others:
Graves disease (autoimmune hyperthyroidism) – in this case it is known as thyroid acropachy
Familial and hereditary clubbing and "pseudoclubbing" (people of African descent often have what appears to be clubbing)
Vascular anomalies of the affected arm such as an axillary artery aneurysm (in unilateral clubbing)Nail clubbing is not specific to chronic obstructive pulmonary disease (COPD).
Therefore, in patients with COPD and significant degrees of clubbing, a search for signs of bronchogenic carcinoma (or other causes of clubbing) might still be indicated. A congenital form has also been recognized. Hypertrophic pulmonary osteoarthropathy
A special form of clubbing is hypertrophic pulmonary osteoarthropathy (HPOA), known in continental Europe as Pierre Marie-Bamberger syndrome. This is the combination of clubbing and thickening of periosteum (connective tissue lining of the bones) and synovium (lining of joints), and is often initially diagnosed as arthritis. It is commonly associated with lung cancer. Primary hypertrophic osteoarthropathy
Primary hypertrophic osteoarthropathy is HPOA without signs of pulmonary disease. This form has a hereditary component, although subtle cardiac abnormalities can occasionally be found. It is known eponymously as the Touraine–Solente–Golé syndrome. This condition has been linked to mutations in the gene on the fourth chromosome (4q33-q34) coding for the enzyme 15-hydroxyprostaglandin dehydrogenase (HPGD); this leads to decreased breakdown of prostaglandin E2 and elevated levels of this substance. Pathogenesis
The exact cause for sporadic clubbing is unknown. Theories as to its cause include:

Vasodilation (i.e., distended blood vessels). Secretion of growth factors (e.g., platelet-derived growth factor and hepatocyte growth factor) from the lungs. Overproduction of prostaglandin E2 by other tissues. Increased entry of megakaryocytes into the systemic circulation. Under normal circumstances in healthy individuals, megakaryocytes that arise from the bone marrow are trapped in the pulmonary capillary bed and broken down before they enter the systemic circulation.